Methods for electrosurgical treatment of intervertebral discs

ABSTRACT

Systems, apparatus and methods for ablation, resection, aspiration, collagen shrinkage and/or hemostasis of tissue and other body structures in open and endoscopic spine surgery. In particular, the present invention includes a channeling technique in which small holes or channels are formed within spinal discs, and thermal energy is applied to the tissue surface immediately surrounding these holes or channels to cause thermal damage to the tissue surface, thereby stiffening the surrounding tissue structure and for reducing the volume of the disc to relieve pressure on the surrounding nerves. High frequency voltage is applied between one or more active electrode(s) and one or more return electrode(s) to volumetrically remove or ablate at least a portion of the disc tissue, and the active electrode(s) are advanced through the space left by the ablated tissue to form a channel, hole, divot or other space in the disc tissue. In addition, the high frequency voltage effects a controlled depth of thermal heating of the tissue surrounding the hole to thermally damage or create a lesion within the tissue surrounding the hole to debulk and/or stiffen the disc structure, thereby relieving neck or back pain.

RELATED APPLICATIONS

The present invention is a continuation-in-part of U.S. patentapplication Ser. No. 09/295,687, filed Apr. 21, 1999 and U.S. patentapplication Ser. Nos. 09/054,323 and 09/268,616, filed Apr. 2, 1998 andMar. 15, 1999, respectively, now U.S. Pat. Nos. 6,063,079 and 6,159,208,respectively each of which are continuation-in-parts of Ser. No.08/990,374, filed Dec. 15, 1997, now U.S. Pat. No. 6,109,268 which is acontinuation-in-part of U.S. patent application Ser. No. 08/485,219,filed on Jun. 7, 1995, now U.S. Pat. No. 5,697,281 the completedisclosures of which are incorporated herein by reference for allpurposes. This application is also a continuation-in-part of U.S. patentapplication Ser. No. 09/026,851, filed Feb. 20, 1999, which is acontinuation-in-part of U.S. patent application Ser. No. 08/690,159,filed Jul. 16, 1996, now U.S. Pat. No. 5,902,272 the complete disclosureof which is incorporated herein by reference for all purposes.

The present invention is related to commonly assigned co-pending U.S.patent application Ser. No. 09/181,926, filed Oct. 28, 1998, U.S. patentapplication Ser. No. 09/130,804, filed Aug. 7, 1998, U.S. patentapplication Ser. No. 09/058,571, filed on Apr. 10, 1998, U.S. patentapplication Ser. No. 09/248,763, filed Feb. 12, 1999, U.S. patentapplication Ser. No. 09/026,698, filed Feb. 20, 1998, U.S. patentapplication Ser. No. 09/074,020, filed on May 6, 1998, U.S. patentapplication Ser. No. 09/010,382, filed Jan. 21, 1998, U.S. patentapplication Ser. No. 09/032,375, filed Feb. 27, 1998, U.S. patentapplication Ser. No. 08/977,845, filed on Nov. 25, 1997, U.S. patentapplication Ser. No. 08/942,580, filed on Oct. 2, 1997, U.S. patentapplication Ser. No. 08/753,227, filed on Nov. 22, 1996, U.S. patentapplication Ser. No. 08/687,792, filed on Jul. 18, 1996, and PCTInternational Application, U.S. National Phase Ser. No. PCT/US94/05168,filed on May 10, 1994, now U.S. Pat. No. 5,697,909, which was acontinuation-in-part of U.S. patent application Ser. No. 08/059,681,filed on May 10, 1993, which was a continuation-in-part of U.S. patentapplication Ser. No. 07/958,977, filed on Oct. 9, 1992 which was acontinuation-in-part of U.S. patent application Ser. No. 07/817,575,filed on Jan. 7, 1992, the complete disclosures of which areincorporated herein by reference for all purposes. The present inventionis also related to commonly assigned U.S. Pat. No. 5,697,882, filed Nov.22, 1995, the complete disclosure of which is incorporated herein byreference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgery,and more particularly to surgical devices and methods which employ highfrequency electrical energy to treat tissue in regions of the spine. Thepresent invention is particularly suited for the treatment of herniateddiscs.

The major causes of persistent, often disabling, back pain aredisruption of the disc annulus, chronic inflammation of the disc (e.g.,herniation), or relative instability of the vertebral bodies surroundinga given disc, such as the instability that often occurs due to adegenerative disease. Intervertebral discs mainly function to cushionand tether the vertebrae, providing flexibility and stability to thepatient's spine. Spinal discs comprise a central hydrostatic cushion,the nucleus pulposus, surrounded by a multi-layered fibrous ligament,the annulus fibrosis. As discs degenerate, they lose their water contentand height, bringing the adjoining vertebrae closer together. Thisresults in a weakening of the shock absorption properties of the discand a narrowing of the nerve openings in the sides of the spine whichmay pinch these nerves. This disc degeneration can eventually cause backand leg pain. Weakness in the annulus from degenerative discs or discinjury can allow fragments of nucleus pulposis from within the discspace to migrate into the spinal canal. There, displaced nucleus orprotrusion of annulus fibrosis, e.g., herniation, may impinge on spinalnerves. The mere proximity of the nucleus pulposis or a damaged annulusto a nerve can cause direct pressure against the nerve, resulting innumbness and weakness of leg muscles.

Often, inflammation from disc herniation can be treated successfully bynon-surgical means, such as rest, therapeutic exercise, oralanti-inflammatory medications or epidural injection of corticosteroids.In some cases, the disc tissue is irreparably damaged, therebynecessitating removal of a portion of the disc or the entire disc toeliminate the source of inflammation and pressure. In more severe cases,the adjacent vertebral bodies must be stabilized following excision ofthe disc material to avoid recurrence of the disabling back pain. Oneapproach to stabilizing the vertebrae, termed spinal fusion, is toinsert an interbody graft or implant into the space vacated by thedegenerative disc. In this procedure, a small amount of bone may begrafted from other portions of the body, such as the hip, and packedinto the implants. This allows the bone to grow through and around theimplant, fusing the vertebral bodies and alleviating the pain.

Until recently, spinal discectomy and fusion procedures resulted inmajor operations and traumatic dissection of muscle and bone removal orbone fusion. To overcome the disadvantages of traditional traumaticspine surgery, minimally invasive spine surgery was developed. Inendoscopic spinal procedures, the spinal canal is not violated andtherefore epidural bleeding with ensuing scarring is minimized orcompletely avoided. In addition, the risk of instability from ligamentand bone removal is generally lower in endoscopic procedures than withopen discectomy. Further, more rapid rehabilitation facilitates fasterrecovery and return to work.

Minimally invasive techniques for the treatment of spinal diseases ordisorders include chemonucleolysis, laser techniques and mechanicaltechniques. These procedures generally require the surgeon to form apassage or operating corridor from the external surface of the patientto the spinal disc(s) for passage of surgical instruments, implants andthe like. Typically, the formation of this operating corridor requiresthe removal of soft tissue, muscle or other types of tissue depending onthe procedure (i.e., laparascopic, thoracoscopic, arthroscopic, back,etc.). This tissue is usually removed with mechanical instruments, suchas pituitary rongeurs, curettes, graspers, cutters, drills,microdebriders and the like. Unfortunately, these mechanical instrumentsgreatly lengthen and increase the complexity of the procedure. Inaddition, these instruments sever blood vessels within this tissue,usually causing profuse bleeding that obstructs the surgeon's view ofthe target site.

Once the operating corridor is established, the nerve root is retractedand a portion or all of the disc is removed with mechanical instruments,such as a pituitary rongeur. In addition to the above problems withmechanical instruments, there are serious concerns because theseinstruments are not precise, and it is often difficult, during theprocedure, to differentiate between the target disc tissue, and otherstructures within the spine, such as bone, cartilage, ligaments, nervesand non-target tissue. Thus, the surgeon must be extremely careful tominimize damage to the cartilage and bone within the spine, and to avoiddamaging nerves, such as the spinal nerves and the dura matersurrounding the spinal cord.

Lasers were initially considered ideal for spine surgery because lasersablate or vaporize tissue with heat, which also acts to cauterize andseal the small blood vessels in the tissue. Unfortunately, lasers areboth expensive and somewhat tedious to use in these procedures. Anotherdisadvantage with lasers is the difficulty in judging the depth oftissue ablation. Since the surgeon generally points and shoots the laserwithout contacting the tissue, he or she does not receive any tactilefeedback to judge how deeply the laser is cutting. Because healthytissue, bones, ligaments and spinal nerves often lie within closeproximity of the spinal disc, it is essential to maintain a minimumdepth of tissue damage, which cannot always be ensured with a laser.

Monopolar radiofrequency devices have been used in limited roles inspine surgery, such as to cauterize severed vessels to improvevisualization. These monopolar devices, however, suffer from thedisadvantage that the electric current will flow through undefined pathsin the patient's body, thereby increasing the risk of unwantedelectrical stimulation to portions of the patient's body. In addition,since the defined path through the patient's body has a relatively highimpedance (because of the large distance or resistivity of the patient'sbody), large voltage differences must typically be applied between thereturn and active electrodes in order to generate a current suitable forablation or cutting of the target tissue. This current, however, mayinadvertently flow along body paths having less impedance than thedefined electrical path, which will substantially increase the currentflowing through these paths, possibly causing damage to or destroyingsurrounding tissue or neighboring peripheral nerves.

Other disadvantages of conventional RF devices, particularly monopolardevices, is nerve stimulation and interference with nerve monitoringequipment in the operating room. In addition, these devices typicallyoperate by creating a voltage difference between the active electrodeand the target tissue, causing an electrical arc to form across thephysical gap between the electrode and tissue. At the point of contactof the electric arcs with tissue, rapid tissue heating occurs due tohigh current density between the electrode and tissue. This high currentdensity causes cellular fluids to rapidly vaporize into steam, therebyproducing a “cutting effect” along the pathway of localized tissueheating. Thus, the tissue is parted along the pathway of evaporatedcellular fluid, inducing undesirable collateral tissue damage in regionssurrounding the target tissue site. This collateral tissue damage oftencauses indiscriminate destruction of tissue, resulting in the loss ofthe proper function of the tissue. In addition, the device does notremove any tissue directly, but rather depends on destroying a zone oftissue and allowing the body to eventually remove the destroyed tissue.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods forselectively applying electrical energy to structures within a patient'sbody, such as tissue within or around the spine. The systems and methodsof the present invention are useful for ablation, resection, aspiration,collagen shrinkage and/or hemostasis of tissue and other body structuresin open and endoscopic spine surgery. In particular, the presentinvention includes a channeling technique in which small holes orchannels are formed within intervertebral discs, and thermal energy isapplied to the tissue surface immediately surrounding these holes orchannels to cause thermal damage to the tissue surface, therebystiffening the surrounding tissue structure and for reducing the volumeof the disc to relieve pressure on the surrounding nerves.

Methods of the present invention include introducing one or more activeelectrode(s) into the patient's spine and positioning the activeelectrode(s) adjacent the target tissue, e.g., a disc. High frequencyvoltage is applied between the active electrode(s) and one or morereturn electrode(s) to volumetrically remove or ablate at least aportion of the target tissue, and the active electrode(s) are advancedthrough the space left by the ablated tissue to form a channel, hole,divot or other space in the disc tissue. The active electrode(s) arethen removed from the channel, and other channels or holes may be formedat suitable locations in the disc. In preferred embodiments, highfrequency voltage is applied to the active electrode(s) as they areremoved from the hole or channel. The high frequency voltage is belowthe threshold for ablation of tissue to effect hemostasis of severedblood vessels within the tissue surface surrounding the hole. Inaddition, the high frequency voltage effects a controlled depth ofthermal heating of the tissue surrounding the hole to thermally damageor create a lesion within the tissue surrounding the hole to debulkand/or stiffen the disc structure, thereby relieving neck or back pain.

In a specific configuration, electrically conductive media, such asisotonic saline or an electrically conductive gel, is delivered to thetarget site within the spine to substantially surround the activeelectrode(s) with the conductive media. The conductive media may bedelivered through an instrument to the specific target site, or theentire target region may be filled with conductive media such that theelectrode terminal(s) are submerged during the procedure. Alternatively,the distal end of the instrument may be dipped or otherwise applied tothe conductive media prior to introduction into the patient's body. Inall of these embodiments, the electrically conductive media is appliedor delivered such that it provides a current flow path between theactive and return electrode(s). In other embodiments, the intracellularconductive fluid in the patient's tissue may be used as a substitutefor, or as a supplement to, the electrically conductive media that isapplied or delivered to the target site. For example, in someembodiments, the instrument is dipped into conductive media to provide asufficient amount of fluid to initiate the requisite conditions forablation. After initiation, the conductive fluid already present in thepatient's tissue is used to sustain these conditions.

In an exemplary embodiment, the active electrode(s) are advanced intothe target disc tissue in the ablation mode, where the high frequencyvoltage is sufficient to ablate or remove the target tissue throughmolecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the activeelectrode(s) is sufficient to vaporize an electrically conductive fluid(e.g., gel, saline and/or intracellular fluid) between the activeelectrode(s) and the tissue. Within the vaporized fluid, a ionizedplasma is formed and charged particles (e.g., electrons) are acceleratedtowards the tissue to cause the molecular breakdown or disintegration ofseveral cell layers of the tissue. This molecular dissociation isaccompanied by the volumetric removal of the tissue. The short range ofthe accelerated charged particles within the plasma layer confines themolecular dissociation process to the surface layer to minimize damageand necrosis to the underlying tissue. This process can be preciselycontrolled to effect the volumetric removal of tissue as thin as 10 to150 microns with minimal heating of, or damage to, surrounding orunderlying tissue structures. A more complete description of thisphenomena is described in commonly assigned U.S. Pat. No. 5,697,882 thecomplete disclosure of which is incorporated herein by reference.

The active electrode(s) are usually removed from the holes or channelsin the subablation or thermal heating mode, where the high frequencyvoltage is below the threshold for ablation as described above, butsufficient to coagulate severed blood vessels and to effect thermaldamage to at least the surface tissue surrounding the holes. In someembodiments, the active electrode(s) are immediately removed from theholes after being placed into the subablation mode. In otherembodiments, the physician may desire to control the rate of removal ofthe active electrode(s) and/or leave the active electrode(s) in the holefor a period of time, e.g., on the order of about 5 to 30 seconds, inthe subablation mode to increase the depth of thermal damage to the disctissue.

In one method, high frequency voltage is applied, in the ablation mode,between one or more active electrode(s) and a return electrode spacedaxially from the active electrode(s), and the active electrode(s) areadvanced into the tissue to form a hole or channel as described above.High frequency voltage is then applied between the return electrode andone or more third electrode(s), in the thermal heating mode, as theelectrosurgical instrument is removed from the hole. In one embodiment,the third electrode is a dispersive return pad on the external surfaceof the skin. In this embodiment, the thermal heating mode is a monopolarmode, in which current flows from the return electrode, through thepatient's body, to the return pad. In other embodiments, the thirdelectrode(s) are located on the electrosurgical instrument and thethermal heating mode is bipolar. In all of the embodiments, the thirdelectrode(s) are designed to increase the depth of current penetrationin the tissue over the ablation mode so as to increase the thermaldamage applied to the disc.

In another method, the third or coagulation electrode is placed in thethermal heating mode at the same time that the active electrode(s) isplaced in the ablation mode. In this embodiment, electric current ispassed from the coagulation electrode, through the tissue surroundingthe hole, to the return electrode at the same time that current ispassing between the active and return electrodes. In a specificconfiguration, this is accomplished by reducing the voltage applied tothe coagulation electrode with a passive or active voltage reductionelement coupled between the power supply and the coagulation electrode.In this manner, when the coagulation electrode is advanced into thetissue, the electric circuit between the coagulation and returnelectrodes is closed by the tissue surrounding the hole, and thusimmediately begins to heat and coagulate this tissue.

In another method, an electrosurgical instrument having an electrodeassembly is dipped into electrically conductive fluid such that theconductive fluid is located around and between both active and returnelectrodes in the electrode assembly. The instrument is then introducedinto the patient's spine either percutaneously or through an openprocedure, and a plurality of holes are formed within the disc asdescribed above. The instrument is removed from each hole in the thermalheating mode to create thermal damage and to coagulate blood vessels.Typically, the instrument will be dipped into the conductive fluid afterbeing removed from each hole to ensure that sufficient conductive fluidexists for plasma formation and to conduct electric current between theactive and return electrodes. This procedure reduces the volume of theintervertebraldisc, which helps to alleviate neck and back pain.

In another aspect of the invention, a method for treating a degenerativeintervertebral disc involves positioning one or more active electrode(s)adjacent to selected nerves embedded in the walls of the disc, andpositioning one or more return electrode(s) in the vicinity of theactive electrode(s) in or on the disc. A sufficient high frequencyvoltage difference is applied between the active and return electrodesto denervate the selected nerves or to break down enzyme systems andpain generating neurotransmitters in the disc, and thus relieve pain. Insome embodiments, the current path between the active and returnelectrode(s) is generated at least in part by an electrically conductivefluid introduced to the target site. In others, the disc tissuecompletes this current path.

In another aspect of the invention, a method for treating degenerativeintervertebral discs involves positioning one or more activeelectrode(s) adjacent to or within the nucleus pulposis, and positioningone or more return electrode(s) in the vicinity of the activeelectrode(s) in or on the disc. A sufficient high frequency voltagedifference is applied between the active and return electrodes to reducewater content of the nucleus pulposis and/or shrink the collagen fiberswithin the nucleus pulposis to tighten the disc. In some embodiments,the current path between the active and return electrode(s) is generatedat least in part by an electrically conductive fluid introduced to thetarget site. In others, the disc tissue completes this current path.

In yet another aspect of the invention, a method for treatingdegenerative intervertebral discs involves positioning one or moreactive electrode(s) adjacent to or within a annular fissure on the innerwall of the annulus fibrosis, and positioning one or more returnelectrode(s) in the vicinity of the active electrode(s) in or around thedisc. A sufficient high frequency voltage difference is applied betweenthe active and return electrodes to weld, seal or shrink the collagenfibers in the annular fissure, thus repairing the fissure. Typically,the voltage is selected to provide sufficient energy to the fissure toraise the tissue temperature to at least about 50° C. to 70° C. for asufficient time to cause the collagen fibers to shrink or weld together.In some embodiments, the current path between the active and returnelectrode(s) is generated at least in part by an electrically conductivefluid introduced to the target site. In others, the disc tissuecompletes this current path.

Systems according to the present invention generally include anelectrosurgical instrument having a shaft with proximal and distal ends,an electrode assembly at the distal end and one or more connectorscoupling the electrode assembly to a source of high frequency electricalenergy. The instrument will comprise a probe or catheter shaft having aproximal end and a distal end which supports the electrode assembly. Theprobe or catheter may assume a wide variety of configurations, with theprimary purpose being to introduce the electrode assembly to thepatient's spine (in an open or endoscopic procedure) and to permit thetreating physician to manipulate the electrode assembly from a proximalend of the shaft. The electrode assembly includes one or more activeelectrode(s) configured for tissue ablation, a return electrode spacedfrom the active electrode(s) on the instrument shaft and a third,coagulation electrode spaced from the return electrode on the instrumentshaft.

The system further includes a power source coupled to the electrodes onthe instrument shaft for applying a high frequency voltage between theactive and return electrodes, and between the coagulation and returnelectrodes, at the same time. In one embodiment, the system comprises avoltage reduction element coupled between the power source and thecoagulation electrode to reduce the voltage applied to the coagulationelectrode. The voltage reduction element will typically comprise apassive element, such as a capacitor, resistor, inductor or the like. Inthe representative embodiment, the power supply will apply a voltage ofabout 150 to 600 volts rms between the active and return electrodes, andthe voltage reduction element will reduce this voltage to about 20 to300 volts rms to the coagulation electrode. In this manner, the voltagedelivered to the coagulation electrode is below the threshold forablation of tissue, but high enough to coagulation and heat the tissue.

The active electrode(s) may comprise a single active electrode, or anelectrode array, extending from an electrically insulating supportmember, typically made of an inorganic material such as ceramic,silicone or glass. The active electrode will usually have a smallerexposed surface area than the return and coagulation electrodes suchthat the current densities are much higher at the active electrode thanat the other electrodes. Preferably, the return and coagulationelectrodes have relatively large, smooth surfaces extending around theinstrument shaft to reduce current densities, thereby minimizing damageto adjacent tissue.

The apparatus may further include a fluid delivery element fordelivering electrically conducting fluid to the active electrode(s) andthe target site. The fluid delivery element may be located on theinstrument, e.g., a fluid lumen or tube, or it may be part of a separateinstrument. Alternatively, an electrically conducting gel or spray, suchas a saline electrolyte or other conductive gel, may be applied to theelectrode assembly or the target site. In this embodiment, the apparatusmay not have a fluid delivery element. In both embodiments, theelectrically conducting fluid will preferably generate a current flowpath between the active electrode(s) and the return electrode(s).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system incorporatinga power supply and an electrosurgical probe for tissue ablation,resection, incision, contraction and for vessel hemostasis according tothe present invention;

FIG. 2 schematically illustrates one embodiment of a power supplyaccording to the present invention;

FIG. 3 illustrates an electrosurgical system incorporating a pluralityof active electrodes and associated current limiting elements;

FIG. 4 is a side view of an electrosurgical probe according to thepresent invention;

FIG. 5 is a view of the distal end portion of the probe of FIG. 2

FIG. 6 is an exploded view of a proximal portion of the electrosurgicalprobe;

FIGS. 7A and 7B are perspective and end views, respectively, of analternative electrosurgical probe incorporating an inner fluid lumen;

FIGS. 8A-8C are cross-sectional views of the distal portions of threedifferent embodiments of an electrosurgical probe according to thepresent invention;

FIGS. 9-13 are end views of alternative embodiments of the probe of FIG.4, incorporating aspiration electrode(s);

FIGS. 14A-14C illustrate an alternative embodiment incorporating ascreen electrode;

FIGS. 15A-15D illustrate four embodiments of electrosurgical probesspecifically designed for treating spinal defects;

FIG. 16 illustrates an electrosurgical system incorporating a dispersivereturn pad for monopolar and/or bipolar operations;

FIG. 17 illustrates a catheter system for electrosurgical treatment ofintervertebral discs according to the present invention;

FIGS. 18-22 illustrate a method of performing a microendoscopicdiscectomy according to the principles of the present invention; and

FIGS. 23-25 illustrates another method of treating a spinal disc withone of the catheters or probes of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention provides systems and methods for selectivelyapplying electrical energy to a target location within or on a patient'sbody, particularly including tissue or other body structures in thespine. These procedures include treating degenerative discs,laminectomy/disketomy procedures for treating herniated discs,decompressive laminectomy for stenosis in the lumbosacral and cervicalspine, localized tears or fissures in the annulus, nucleotomy, discfusion procedures, medial facetectomy, posterior lumbosacral andcervical spine fusions, treatment of scoliosis associated with vertebraldisease, foraminotomies to remove the roof of the intervertebralforamina to relieve nerve root compression and anterior cervical andlumbar discectomies. These procedures may be performed through openprocedures, or using minimally invasive techniques, such asthoracoscopy, arthroscopy, laparascopy or the like.

The present invention involves techniques for treating discabnormalities with RF energy. In some embodiments, RF energy is used toablate, debulk and/or stiffen the tissue structure of the disc to reducethe volume of the disc, thereby relieving neck and back pain. In oneaspect of the invention, spinal disc tissue is volumetrically removed orablated to form holes, channels, divots or other spaces within the disc.In this procedure, a high frequency voltage difference is appliedbetween one or more active electrode(s) and one or more returnelectrode(s) to develop high electric field intensities in the vicinityof the target tissue. The high electric field intensities adjacent theactive electrode(s) lead to electric field induced molecular breakdownof target tissue through molecular dissociation (rather than thermalevaporation or carbonization). Applicant believes that the tissuestructure is volumetrically removed through molecular disintegration oflarger organic molecules into smaller molecules and/or atoms, such ashydrogen, oxygen, oxides of carbon, hydrocarbons and nitrogen compounds.This molecular disintegration completely removes the tissue structure,as opposed to dehydrating the tissue material by the removal of liquidwithin the cells of the tissue, as is typically the case withelectrosurgical desiccation and vaporization.

The high electric field intensities may be generated by applying a highfrequency voltage that is sufficient to vaporize an electricallyconducting fluid over at least a portion of the active electrode(s) inthe region between the distal tip of the active electrode(s) and thetarget tissue. The electrically conductive fluid may be a liquid or gas,such as isotonic saline, blood or intracellular fluid, delivered to, oralready present at, the target site, or a viscous fluid, such as a gel,applied to the target site. Since the vapor layer or vaporized regionhas a relatively high electrical impedance, it increases the voltagedifferential between the electrode terminal tip and the tissue andcauses ionization within the vapor layer due to the presence of anionizable species (e.g., sodium when isotonic saline is the electricallyconducting fluid). This ionization, under the conditions describedherein, induces the discharge of energetic electrons and photons fromthe vapor layer and to the surface of the target tissue. This energy maybe in the form of energetic photons (e.g., ultraviolet radiation),energetic particles (e.g., electrons or ions) or a combination thereof.A more detailed description of this phenomena, termed Coblation™ can befound in commonly assigned U.S. Pat. No. 5,697,882 the completedisclosure of which is incorporated herein by reference.

Applicant believes that the principle mechanism of tissue removal in theCoblation™ mechanism of the present invention is energetic electrons orions that have been energized in a plasma adjacent to the activeelectrode(s). When a liquid is heated enough that atoms vaporize off thesurface faster than they recondense, a gas is formed. When the gas isheated enough that the atoms collide with each other and knock theirelectrons off in the process, an ionized gas or plasma is formed (theso-called “fourth state of matter”). A more complete description ofplasma can be found in Plasma Physics, by R. J. Goldston and P. H.Rutherford of the Plasma Physics Laboratory of Princeton University(1995). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 1020 atoms/cm3 for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Once the ionic particles in the plasmalayer have sufficient energy, they accelerate towards the target tissue.Energy evolved by the energetic electrons (e.g., 3.5 eV to 5 eV) cansubsequently bombard a molecule and break its bonds, dissociating amolecule into free radicals, which then combine into final gaseous orliquid species.

Plasmas may be formed by heating a gas and ionizing the gas by drivingan electric current through it, or by shining radio waves into the gas.Generally, these methods of plasma formation give energy to freeelectrons in the plasma directly, and then electron-atom collisionsliberate more electrons, and the process cascades until the desireddegree of ionization is achieved. Often, the electrons carry theelectrical current or absorb the radio waves and, therefore, are hotterthan the ions. Thus, in applicant's invention, the electrons, which arecarried away from the tissue towards the return electrode, carry most ofthe plasma's heat with them, allowing the ions to break apart the tissuemolecules in a substantially non-thermal manner.

In some embodiments, the present invention applies high frequency (RF)electrical energy in an electrically conducting media environment toremove (i.e., resect, cut or ablate) a tissue structure and to sealtransected vessels within the region of the target tissue. The presentinvention may also be useful for sealing larger arterial vessels, e.g.,on the order of about 1 mm in diameter. In some embodiments, a highfrequency power supply is provided having an ablation mode, wherein afirst voltage is applied to an electrode terminal sufficient to effectmolecular dissociation or disintegration of the tissue, and acoagulation mode, wherein a second, lower voltage is applied to anelectrode terminal (either the same or a different electrode) sufficientto achieve hemostasis of severed vessels within the tissue. In otherembodiments, an electrosurgical instrument is provided having one ormore coagulation electrode(s) configured for sealing a severed vessel,such as an arterial vessel, and one or more electrode terminalsconfigured for either contracting the collagen fibers within the tissueor removing (ablating) the tissue, e.g., by applying sufficient energyto the tissue to effect molecular dissociation. In the latterembodiments, the coagulation electrode(s) may be configured such that asingle voltage can be applied to coagulate with the coagulationelectrode(s), and to ablate with the electrode terminal(s). In otherembodiments, the power supply is combined with the coagulationinstrument such that the coagulation electrode is used when the powersupply is in the coagulation mode (low voltage), and the electrodeterminal(s) are used when the power supply is in the ablation mode(higher voltage).

In one method of the present invention, one or more electrode terminalsare brought into close proximity to tissue at a target site, and thepower supply is activated in the ablation mode such that sufficientvoltage is applied between the electrode terminals and the returnelectrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, vessels withinthe tissue will be severed. Smaller vessels will be automatically sealedwith the system and method of the present invention. Larger vessels, andthose with a higher flow rate, such as arterial vessels, may not beautomatically sealed in the ablation mode. In these cases, the severedvessels may be sealed by activating a control (e.g., a foot pedal) toreduce the voltage of the power supply into the coagulation mode. Inthis mode, the electrode terminals may be pressed against the severedvessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent instrument may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

In some embodiments of the present invention, the tissue is purposelydamaged in a thermal heating mode to create necrosed or scarred tissueat the tissue surface. The high frequency voltage in the thermal heatingmode is below the threshold of ablation as described above, butsufficient to cause some thermal damage to the tissue immediatelysurrounding the electrodes without vaporizing or otherwise debulkingthis tissue in situ. Typically, it is desired to achieve a tissuetemperature in the range of about 60° C. to 100° C. to a depth of about0.2 to 5 mm, usually about 1 to 2 mm. The voltage required for thisthermal damage will partly depend on the electrode configurations, theconductivity of the area immediately surrounding the electrodes, thetime period in which the voltage is applied and the depth of tissuedamage desired. With the electrode configurations described in thisapplication (e.g., FIGS. 15A-15D), the voltage level for thermal heatingwill usually be in the range of about 20 to 300 volts rms, preferablyabout 60 to 200 volts rms. The peak-to-peak voltages for thermal heatingwith a square wave form having a crest factor of about 2 are typicallyin the range of about 40 to 600 volts peak-to-peak, preferably about 120to 400 volts peak-to-peak. The higher the voltage is within this range,the less time required. If the voltage is too high, however, the surfacetissue may be vaporized, debulked or ablated, which is undesirable.

In other embodiments, the present invention may be used for treatingdegenerative discs with fissures or tears. In these embodiments, theactive and return electrode(s) are positioned in or around the innerwall of the disc annulus such that the active electrode is adjacent tothe fissure. High frequency voltage is applied between the active andreturn electrodes to heat the fissure and shrink the collagen fibers andcreate a seal or weld within the inner wall, thereby helping to closethe fissure in the annulus. In these embodiments, the return electrodewill typically be positioned proximally from the active electrode(s) onthe instrument shaft, and an electrically conductive fluid will beapplied to the target site to create the necessary current path betweenthe active and return electrodes. In alternative embodiments, the disctissue may complete this electrically conductive path.

The present invention is also useful for removing or ablating tissuearound nerves, such as spinal, peripheral or cranial nerves. One of thesignificant drawbacks with the prior art shavers or microdebriders,conventional electrosurgical devices and lasers is that these devices donot differentiate between the target tissue and the surrounding nervesor bone. Therefore, the surgeon must be extremely careful during theseprocedures to avoid damage to the bone or nerves within and around thetarget site. In the present invention, the Coblation™ process forremoving tissue results in extremely small depths of collateral tissuedamage as discussed above. This allows the surgeon to remove tissueclose to a nerve without causing collateral damage to the nerve fibers.

In addition to the generally precise nature of the novel mechanisms ofthe present invention, applicant has discovered an additional method ofensuring that adjacent nerves are not damaged during tissue removal.According to the present invention, systems and methods are provided fordistinguishing between the fatty tissue immediately surrounding nervefibers and the normal tissue that is to be removed during the procedure.Nerves usually comprise a connective tissue sheath, or epineurium,enclosing the bundles of nerve fibers, each bundle being surrounded byits own sheath of connective tissue (the perineurium) to protect thesenerve fibers. The outer protective tissue sheath or epineurium typicallycomprises a fatty tissue (e.g., adipose tissue) having substantiallydifferent electrical properties than the normal target tissue, such asthe turbinates, polyps, mucus tissue or the like, that are, for example,removed from the nose during sinus procedures. The system of the presentinvention measures the electrical properties of the tissue at the tip ofthe probe with one or more electrode terminal(s). These electricalproperties may include electrical conductivity at one, several or arange of frequencies (e.g., in the range from 1 kHz to 100 MHz),dielectric constant, capacitance or combinations of these. In thisembodiment, an audible signal may be produced when the sensingelectrode(s) at the tip of the probe detects the fatty tissuesurrounding a nerve, or direct feedback control can be provided to onlysupply power to the electrode terminal(s) either individually or to thecomplete array of electrodes, if and when the tissue encountered at thetip or working end of the probe is normal tissue based on the measuredelectrical properties.

In one embodiment, the current limiting elements (discussed in detailabove) are configured such that the electrode terminals will shut downor turn off when the electrical impedance reaches a threshold level.When this threshold level is set to the impedance of the fatty tissuesurrounding nerves, the electrode terminals will shut off whenever theycome in contact with, or in close proximity to, nerves. Meanwhile, theother electrode terminals, which are in contact with or in closeproximity to tissue, will continue to conduct electric current to thereturn electrode. This selective ablation or removal of lower impedancetissue in combination with the Coblation™ mechanism of the presentinvention allows the surgeon to precisely remove tissue around nerves orbone. Applicant has found that the present invention is capable ofvolumetrically removing tissue closely adjacent to nerves withoutimpairment the function of the nerves, and without significantlydamaging the tissue of the epineurium. One of the significant drawbackswith the prior art microdebriders, conventional electrosurgical devicesand lasers is that these devices do not differentiate between the targettissue and the surrounding nerves or bone. Therefore, the surgeon mustbe extremely careful during these procedures to avoid damage to the boneor nerves within and around the nasal cavity. In the present invention,the Coblation™ process for removing tissue results in extremely smalldepths of collateral tissue damage as discussed above. This allows thesurgeon to remove tissue close to a nerve without causing collateraldamage to the nerve fibers.

In addition to the above, applicant has discovered that the Coblation™mechanism of the present invention can be manipulated to ablate orremove certain tissue structures, while having little effect on othertissue structures. As discussed above, the present invention uses atechnique of vaporizing electrically conductive fluid to form a plasmalayer or pocket around the electrode terminal(s), and then inducing thedischarge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 1020 atoms/cm3 for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

The energy evolved by the energetic electrons may be varied by adjustinga variety of factors, such as: the number of electrode terminals;electrode size and spacing; electrode surface area; asperities and sharpedges on the electrode surfaces; electrode materials; applied voltageand power; current limiting means, such as inductors; electricalconductivity of the fluid in contact with the electrodes; density of thefluid; and other factors. Accordingly, these factors can be manipulatedto control the energy level of the excited electrons. Since differenttissue structures have different molecular bonds, the present inventioncan be configured to break the molecular bonds of certain tissue, whilehaving too low an energy to break the molecular bonds of other tissue.For example, fatty tissue, (e.g., adipose) tissue has double bonds thatrequire a substantially higher energy level than 4 to 5 eV to break(typically on the order of about 8 eV). Accordingly, the presentinvention in its current configuration generally does not ablate orremove such fatty tissue. Of course, factors may be changed such thatthese double bonds can also be broken in a similar fashion as the singlebonds (e.g., increasing voltage or changing the electrode configurationto increase the current density at the electrode tips). A more completedescription of this phenomena can be found in co-pending U.S. patentapplication Ser. No. 09/032,375, filed Feb. 27, 1998, the completedisclosure of which is incorporated herein by reference.

The present invention also provides systems, apparatus and methods forselectively removing tumors, e.g., facial tumors, or other undesirablebody structures while minimizing the spread of viable cells from thetumor. Conventional techniques for removing such tumors generally resultin the production of smoke in the surgical setting, termed anelectrosurgical or laser plume, which can spread intact, viablebacterial or viral particles from the tumor or lesion to the surgicalteam or to other portions of the patient's body. This potential spreadof viable cells or particles has resulted in increased concerns over theproliferation of certain debilitating and fatal diseases, such ashepatitis, herpes, HIV and papillomavirus. In the present invention,high frequency voltage is applied between the electrode terminal(s) andone or more return electrode(s) to volumetrically remove at least aportion of the tissue cells in the tumor through the dissociation ordisintegration of organic molecules into non-viable atoms and molecules.Specifically, the present invention converts the solid tissue cells intonon-condensable gases that are no longer intact or viable, and thus, notcapable of spreading viable tumor particles to other portions of thepatient's brain or to the surgical staff. The high frequency voltage ispreferably selected to effect controlled removal of these tissue cellswhile minimizing substantial tissue necrosis to surrounding orunderlying tissue. A more complete description of this phenomena can befound in co-pending U.S. patent application Ser. No. 09/109,219, filedJun. 30, 1998, the complete disclosure of which is incorporated hereinby reference.

In other procedures, it may be desired to shrink or contract collagenconnective tissue within the disc. In these procedures, the RF energyheats the disc tissue directly by virtue of the electrical current flowtherethrough, and/or indirectly through the exposure of the tissue tofluid heated by RF energy, to elevate the tissue temperature from normalbody temperatures (e.g., 37° C.) to temperatures in the range of 45° C.to 90° C., preferably in the range from about 60° C. to 70° C. Thermalshrinkage of collagen fibers occurs within a small temperature rangewhich, for mammalian collagen is in the range from 60° C. to 70° C.(Deak, G., et al., “The Thermal Shrinkage Process of Collagen Fibers asRevealed by Polarization Optical Analysis of Topooptical StainingReactions,” Acta Morphologica Acad. Sci. of Hungary, Vol. 15(2), pp195-208, 1967). Collagen fibers typically undergo thermal shrinkage inthe range of 60° C. to about 70° C. Previously reported research hasattributed thermal shrinkage of collagen to the cleaving of the internalstabilizing cross-linkages within the collagen matrix (Deak, ibid). Ithas also been reported that when the collagen temperature is increasedabove 70° C., the collagen matrix begins to relax again and theshrinkage effect is reversed resulting in no net shrinkage (Allain, J.C., et al., “Isometric Tensions Developed During the HydrothermalSwelling of Rat Skin,” Connective Tissue Research, Vol. 7, pp 127-133,1980). Consequently, the controlled heating of tissue to a precise depthis critical to the achievement of therapeutic collagen shrinkage. A moredetailed description of collagen shrinkage can be found in U.S. patentapplication Ser. No. 08/942,580 filed on Oct. 2, 1997.

The preferred depth of heating to effect the shrinkage of collagen inthe heated region (i.e., the depth to which the tissue is elevated totemperatures between 60° C. to 70° C.) generally depends on (1) thethickness of the disc, (2) the location of nearby structures (e.g.,nerves) that should not be exposed to damaging temperatures, and/or (3)the location of the collagen tissue layer within which therapeuticshrinkage is to be effected. The depth of heating is usually in therange from 1.0 to 5.0 mm.

The electrosurgical probe or catheter will comprise a shaft or ahandpiece having a proximal end and a distal end which supports one ormore electrode terminal(s). The shaft or handpiece may assume a widevariety of configurations, with the primary purpose being tomechanically support the active electrode and permit the treatingphysician to manipulate the electrode from a proximal end of the shaft.The shaft may be rigid or flexible, with flexible shafts optionallybeing combined with a generally rigid external tube for mechanicalsupport. Flexible shafts may be combined with pull wires, shape memoryactuators, and other known mechanisms for effecting selective deflectionof the distal end of the shaft to facilitate positioning of theelectrode array. The shaft will usually include a plurality of wires orother conductive elements running axially therethrough to permitconnection of the electrode array to a connector at the proximal end ofthe shaft.

For endoscopic procedures within the spine, the shaft will have asuitable diameter and length to allow the surgeon to reach the targetsite (e.g., a disc) by delivering the shaft through the thoracic cavity,the abdomen or the like. Thus, the shaft will usually have a length inthe range of about 5.0 to 30.0 cm, and a diameter in the range of about0.2 mm to about 20 mm. Alternatively, the shaft may be delivereddirectly through the patient's back in a posterior approach, which wouldconsiderably reduce the required length of the shaft. In any of theseembodiments, the shaft may also be introduced through rigid or flexibleendoscopes. Alternatively, the shaft may be a flexible catheter that isintroduced through a percutaneous penetration in the patient. Specificshaft designs will be described in detail in connection with the figureshereinafter.

In an alternative embodiment, the probe may comprise a long, thin needle(e.g., on the order of about 1 mm in diameter or less) that can bepercutaneously introduced through the patient's back directly into thespine. The needle will include one or more active electrode(s) forapplying electrical energy to tissues within the spine. The needle mayinclude one or more return electrode(s), or the return electrode may bepositioned on the patient's back, as a dispersive pad. In eitherembodiment, sufficient electrical energy is applied through the needleto the active electrode(s) to either shrink the collagen fibers withinthe spinal disc, or to ablate tissue within the disc.

The electrosurgical instrument may also be a catheter that is deliveredpercutaneously and/or endoluminally into the patient by insertionthrough a conventional or specialized guide catheter, or the inventionmay include a catheter having an active electrode or electrode arrayintegral with its distal end. The catheter shaft may be rigid orflexible, with flexible shafts optionally being combined with agenerally rigid external tube for mechanical support. Flexible shaftsmay be combined with pull wires, shape memory actuators, and other knownmechanisms for effecting selective deflection of the distal end of theshaft to facilitate positioning of the electrode or electrode array. Thecatheter shaft will usually include a plurality of wires or otherconductive elements running axially therethrough to permit connection ofthe electrode or electrode array and the return electrode to a connectorat the proximal end of the catheter shaft. The catheter shaft mayinclude a guide wire for guiding the catheter to the target site, or thecatheter may comprise a steerable guide catheter. The catheter may alsoinclude a substantially rigid distal end portion to increase the torquecontrol of the distal end portion as the catheter is advanced furtherinto the patient's body. Specific shaft designs will be described indetail in connection with the figures hereinafter.

The electrode terminal(s) are preferably supported within or by aninorganic insulating support positioned near the distal end of theinstrument shaft. The return electrode may be located on the instrumentshaft, on another instrument or on the external surface of the patient(i.e., a dispersive pad). The close proximity of nerves and othersensitive tissue in and around the spinal cord, however, makes a bipolardesign more preferable because this minimizes the current flow throughnon-target tissue and surrounding nerves. Accordingly, the returnelectrode is preferably either integrated with the instrument body, oranother instrument located in close proximity thereto. The proximal endof the instrument(s) will include the appropriate electrical connectionsfor coupling the return electrode(s) and the electrode terminal(s) to ahigh frequency power supply, such as an electrosurgical generator.

In some embodiments, the active electrode(s) have an active portion orsurface with surface geometries shaped to promote the electric fieldintensity and associated current density along the leading edges of theelectrodes. Suitable surface geometries may be obtained by creatingelectrode shapes that include preferential sharp edges, or by creatingasperities or other surface roughness on the active surface(s) of theelectrodes. Electrode shapes according to the present invention caninclude the use of formed wire (e.g., by drawing round wire through ashaping die) to form electrodes with a variety of cross-sectionalshapes, such as square, rectangular, L or V shaped, or the like.Electrode edges may also be created by removing a portion of theelongate metal electrode to reshape the cross-section. For example,material can be ground along the length of a round or hollow wireelectrode to form D or C shaped wires, respectively, with edges facingin the cutting direction. Alternatively, material can be removed atclosely spaced intervals along the electrode length to form transversegrooves, slots, threads or the like along the electrodes.

Additionally or alternatively, the active electrode surface(s) may bemodified through chemical, electrochemical or abrasive methods to createa multiplicity of surface asperities on the electrode surface. Thesesurface asperities will promote high electric field intensities betweenthe active electrode surface(s) and the target tissue to facilitateablation or cutting of the tissue. For example, surface asperities maybe created by etching the active electrodes with etchants having a Phless than 7.0 or by using a high velocity stream of abrasive particles(e.g., grit blasting) to create asperities on the surface of anelongated electrode. A more detailed description of such electrodeconfigurations can be found in U.S. Pat. No. 5,843,019, the completedisclosure of which is incorporated herein by reference.

The return electrode is typically spaced proximally from the activeelectrode(s) a suitable distance to avoid electrical shorting betweenthe active and return electrodes in the presence of electricallyconductive fluid. In most of the embodiments described herein, thedistal edge of the exposed surface of the return electrode is spacedabout 0.5 to 25 mm from the proximal edge of the exposed surface of theactive electrode(s), preferably about 1.0 to 5.0 mm. Of course, thisdistance may vary with different voltage ranges, conductive fluids, anddepending on the proximity of tissue structures to active and returnelectrodes. The return electrode will typically have an exposed lengthin the range of about 1 to 20 mm.

The current flow path between the electrode terminals and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a viscous fluid, such as anelectrically conductive gel) or by directing an electrically conductingfluid along a fluid path to the target site (i.e., a liquid, such asisotonic saline, hypotonic saline or a gas, such as argon). Theconductive gel may also be delivered to the target site to achieve aslower more controlled delivery rate of conductive fluid. In addition,the viscous nature of the gel may allow the surgeon to more easilycontain the gel around the target site (e.g., rather than attempting tocontain isotonic saline). A more complete description of an exemplarymethod of directing electrically conducting fluid between the active andreturn electrodes is described in U.S. Pat. No. 5,697,281, previouslyincorporated herein by reference. Alternatively, the body's naturalconductive fluids, such as blood or intracellular saline, may besufficient to establish a conductive path between the returnelectrode(s) and the electrode terminal(s), and to provide theconditions for establishing a vapor layer, as described above. However,conductive fluid that is introduced into the patient is generallypreferred over blood because blood will tend to coagulate at certaintemperatures. In addition, the patient's blood may not have sufficientelectrical conductivity to adequately form a plasma in someapplications. Advantageously, a liquid electrically conductive fluid(e.g., isotonic saline) may be used to concurrently “bathe” the targettissue surface to provide an additional means for removing any tissue,and to cool the region of the target tissue ablated in the previousmoment.

The power supply may include a fluid interlock for interrupting power tothe electrode terminal(s) when there is insufficient conductive fluidaround the electrode terminal(s). This ensures that the instrument willnot be activated when conductive fluid is not present, minimizing thetissue damage that may otherwise occur. A more complete description ofsuch a fluid interlock can be found in commonly assigned, co-pendingU.S. patent application Ser. No. 09/058,336, filed Apr. 10, 1998, thecomplete disclosure of which is incorporated herein by reference.

In some procedures, it may also be necessary to retrieve or aspirate theelectrically conductive fluid and/or the non-condensible gaseousproducts of ablation. In addition, it may be desirable to aspirate smallpieces of tissue or other body structures that are not completelydisintegrated by the high frequency energy, or other fluids at thetarget site, such as blood, mucus, the gaseous products of ablation,etc. Accordingly, the system of the present invention may include one ormore suction lumen(s) in the instrument, or on another instrument,coupled to a suitable vacuum source for aspirating fluids from thetarget site. In addition, the invention may include one or moreaspiration electrode(s) coupled to the distal end of the suction lumenfor ablating, or at least reducing the volume of, non-ablated tissuefragments that are aspirated into the lumen. The aspiration electrode(s)function mainly to inhibit clogging of the lumen that may otherwiseoccur as larger tissue fragments are drawn therein. The aspirationelectrode(s) may be different from the ablation electrode terminal(s),or the same electrode(s) may serve both functions. A more completedescription of instruments incorporating aspiration electrode(s) can befound in commonly assigned, co-pending patent application entitled“Systems And Methods For Tissue Resection, Ablation And Aspiration”,filed Jan. 21, 1998, the complete disclosure of which is incorporatedherein by reference.

As an alternative or in addition to suction, it may be desirable tocontain the excess electrically conductive fluid, tissue fragmentsand/or gaseous products of ablation at or near the target site with acontainment apparatus, such as a basket, retractable sheath or the like.This embodiment has the advantage of ensuring that the conductive fluid,tissue fragments or ablation products do not flow through the patient'svasculature or into other portions of the body. In addition, it may bedesirable to limit the amount of suction to limit the undesirable effectsuction may have on hemostasis of severed blood vessels.

The present invention may use a single active electrode terminal or anarray of electrode terminals spaced around the distal surface of acatheter or probe. In the latter embodiment, the electrode array usuallyincludes a plurality of independently current-limited and/orpower-controlled electrode terminals to apply electrical energyselectively to the target tissue while limiting the unwanted applicationof electrical energy to the surrounding tissue and environment resultingfrom power dissipation into surrounding electrically conductive fluids,such as blood, normal saline, and the like. The electrode terminals maybe independently current-limited by isolating the terminals from eachother and connecting each terminal to a separate power source that isisolated from the other electrode terminals. Alternatively, theelectrode terminals may be connected to each other at either theproximal or distal ends of the catheter to form a single wire thatcouples to a power source.

In one configuration, each individual electrode terminal in theelectrode array is electrically insulated from all other electrodeterminals in the array within said instrument and is connected to apower source which is isolated from each of the other electrodeterminals in the array or to circuitry which limits or interruptscurrent flow to the electrode terminal when low resistivity material(e.g., blood, electrically conductive saline irrigant or electricallyconductive gel) causes a lower impedance path between the returnelectrode and the individual electrode terminal. The isolated powersources for each individual electrode terminal may be separate powersupply circuits having internal impedance characteristics which limitpower to the associated electrode terminal when a low impedance returnpath is encountered. By way of example, the isolated power source may bea user selectable constant current source. In this embodiment, lowerimpedance paths will automatically result in lower resistive heatinglevels since the heating is proportional to the square of the operatingcurrent times the impedance. Alternatively, a single power source may beconnected to each of the electrode terminals through independentlyactuatable switches, or by independent current limiting elements, suchas inductors, capacitors, resistors and/or combinations thereof. Thecurrent limiting elements may be provided in the instrument, connectors,cable, controller or along the conductive path from the controller tothe distal tip of the instrument. Alternatively, the resistance and/orcapacitance may occur on the surface of the active electrode terminal(s)due to oxide layers which form selected electrode terminals (e.g.,titanium or a resistive coating on the surface of metal, such asplatinum).

The tip region of the instrument may comprise many independent electrodeterminals designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual electrode terminal andthe return electrode to a power source having independently controlledor current limited channels. The return electrode(s) may comprise asingle tubular member of conductive material proximal to the electrodearray at the tip which also serves as a conduit for the supply of theelectrically conducting fluid between the active and return electrodes.Alternatively, the instrument may comprise an array of return electrodesat the distal tip of the instrument (together with the activeelectrodes) to maintain the electric current at the tip. The applicationof high frequency voltage between the return electrode(s) and theelectrode array results in the generation of high electric fieldintensities at the distal tips of the electrode terminals withconduction of high frequency current from each individual electrodeterminal to the return electrode. The current flow from each individualelectrode terminal to the return electrode(s) is controlled by eitheractive or passive means, or a combination thereof, to deliver electricalenergy to the surrounding conductive fluid while minimizing energydelivery to surrounding (non-target) tissue.

The application of a high frequency voltage between the returnelectrode(s) and the electrode terminal(s) for appropriate timeintervals effects cutting, removing, ablating, shaping, contracting orotherwise modifying the target tissue. In some embodiments of thepresent invention, the tissue volume over which energy is dissipated(i.e., a high current density exists) may be more precisely controlled,for example, by the use of a multiplicity of small electrode terminalswhose effective diameters or principal dimensions range from about 10 mmto 0.01 mm, preferably from about 2 mm to 0.05 mm, and more preferablyfrom about 1 mm to 0.1 mm. In this embodiment, electrode areas for bothcircular and non-circular terminals will have a contact area (perelectrode terminal) below 50 mm2 for electrode arrays and as large as 75mm2 for single electrode embodiments. In multiple electrode arrayembodiments, the contact area of each electrode terminal is typically inthe range from 0.0001 mm2 to 1 mm2, and more preferably from 0.001 mm2to 0.5 mm2. The circumscribed area of the electrode array or electrodeterminal is in the range from 0.25 mm2 to 75 mm2, preferably from 0.5mm2 to 40 mm2. In multiple electrode embodiments, the array will usuallyinclude at least two isolated electrode terminals, often at least fiveelectrode terminals, often greater than 10 electrode terminals and even50 or more electrode terminals, disposed over the distal contactsurfaces on the shaft. The use of small diameter electrode terminalsincreases the electric field intensity and reduces the extent or depthof tissue heating as a consequence of the divergence of current fluxlines which emanate from the exposed surface of each electrode terminal.

The area of the tissue treatment surface can vary widely, and the tissuetreatment surface can assume a variety of geometries, with particularareas and geometries being selected for specific applications. Thegeometries can be planar, concave, convex, hemispherical, conical,linear “in-line” array or virtually any other regular or irregularshape. Most commonly, the active electrode(s) or electrode terminal(s)will be formed at the distal tip of the electrosurgical instrumentshaft, frequently being planar, disk-shaped, or hemispherical surfacesfor use in reshaping procedures or being linear arrays for use incutting. Alternatively or additionally, the active electrode(s) may beformed on lateral surfaces of the electrosurgical instrument shaft(e.g., in the manner of a spatula), facilitating access to certain bodystructures in endoscopic procedures.

In some embodiments, the electrode support and the fluid outlet may berecessed from an outer surface of the instrument or handpiece to confinethe electrically conductive fluid to the region immediately surroundingthe electrode support. In addition, the shaft may be shaped so as toform a cavity around the electrode support and the fluid outlet. Thishelps to assure that the electrically conductive fluid will remain incontact with the electrode terminal(s) and the return electrode(s) tomaintain the conductive path therebetween. In addition, this will helpto maintain a vapor layer and subsequent plasma layer between theelectrode terminal(s) and the tissue at the treatment site throughoutthe procedure, which reduces the thermal damage that might otherwiseoccur if the vapor layer were extinguished due to a lack of conductivefluid. Provision of the electrically conductive fluid around the targetsite also helps to maintain the tissue temperature at desired levels.

In other embodiments, the active electrodes are spaced from the tissue asufficient distance to minimize or avoid contact between the tissue andthe vapor layer formed around the active electrodes. In theseembodiments, contact between the heated electrons in the vapor layer andthe tissue is minimized as these electrons travel from the vapor layerback through the conductive fluid to the return electrode. The ionswithin the plasma, however, will have sufficient energy, under certainconditions such as higher voltage levels, to accelerate beyond the vaporlayer to the tissue. Thus, the tissue bonds are dissociated or broken asin previous embodiments, while minimizing the electron flow, and thusthe thermal energy, in contact with the tissue.

The electrically conducting fluid should have a threshold conductivityto provide a suitable conductive path between the return electrode andthe electrode terminal(s). The electrical conductivity of the fluid (inunits of milliSiemans per centimeter or mS/cm) will usually be greaterthan 0.2 mS/cm, preferably will be greater than 2 mS/cm and morepreferably greater than 10 mS/cm. In an exemplary embodiment, theelectrically conductive fluid is isotonic saline, which has aconductivity of about 17 mS/cm. Applicant has found that a moreconductive fluid, or one with a higher ionic concentration, will usuallyprovide a more aggressive ablation rate. For example, a saline solutionwith higher levels of sodium chloride than conventional saline (which ison the order of about 0.9% sodium chloride) e.g., on the order ofgreater than 1% or between about 3% and 20%, may be desirable.Alternatively, the invention may be used with different types ofconductive fluids that increase the power of the plasma layer by, forexample, increasing the quantity of ions in the plasma, or by providingions that have higher energy levels than sodium ions. For example, thepresent invention may be used with elements other than sodium, such aspotassium, magnesium, calcium and other metals near the left end of theperiodic chart. In addition, other electronegative elements may be usedin place of chlorine, such as fluorine.

The voltage difference applied between the return electrode(s) and theelectrode terminal(s) will be at high or radio frequency, typicallybetween about 5 kHz and 20 MHz, usually being between about 30 kHz and2.5 MHz, preferably being between about 50 kHz and 500 kHz, often lessthan 350 kHz, and often between about 100 kHz and 200 kHz. In someapplications, applicant has found that a frequency of about 100 kHz isuseful because the tissue impedance is much greater at this frequency.In other applications, such as procedures in or around the heart or headand neck, higher frequencies may be desirable (e.g., 400-600 kHz) tominimize low frequency current flow into the heart or the nerves of thehead and neck. The RMS (root mean square) voltage applied will usuallybe in the range from about 5 volts to 1000 volts, preferably being inthe range from about 10 volts to 500 volts, often between about 150 to400 volts depending on the electrode terminal size, the operatingfrequency and the operation mode of the particular procedure or desiredeffect on the tissue (i.e., contraction, coagulation, cutting orablation). Typically, the peak-to-peak voltage for ablation or cuttingwith a square wave form will be in the range of 10 to 2000 volts andpreferably in the range of 100 to 1800 volts and more preferably in therange of about 300 to 1500 volts, often in the range of about 300 to 800volts peak to peak (again, depending on the electrode size, number ofelectrons, the operating frequency and the operation mode). Lowerpeak-to-peak voltages will be used for tissue coagulation, thermalheating of tissue, or collagen contraction and will typically be in therange from 50 to 1500, preferably 100 to 1000 and more preferably 120 to400 volts peak-to-peak (again, these values are computed using a squarewave form). Higher peak-to-peak voltages, e.g., greater than about 800volts peak-to-peak, may be desirable for ablation of harder material,such as bone, depending on other factors, such as the electrodegeometries and the composition of the conductive fluid.

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 to 20 Hz). In addition, the duty cycle (i.e.,cumulative time in any one-second interval that energy is applied) is onthe order of about 50% for the present invention, as compared withpulsed lasers which typically have a duty cycle of about 0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the instrument tip. The power source allows theuser to select the voltage level according to the specific requirementsof a particular neurosurgery procedure, cardiac surgery, arthroscopicsurgery, dermatological procedure, ophthalmic procedures, open surgeryor other endoscopic surgery procedure. For cardiac procedures andpotentially for neurosurgery, the power source may have an additionalfilter, for filtering leakage voltages at frequencies below 100 kHz,particularly voltages around 60 kHz. Alternatively, a power sourcehaving a higher operating frequency, e.g., 300 to 600 kHz may be used incertain procedures in which stray low frequency currents may beproblematic. A description of one suitable power source can be found inco-pending patent applications Ser. Nos. 09/058,571 and 09/058,336,filed Apr. 10, 1998, the complete disclosure of both applications areincorporated herein by reference for all purposes.

The power source may be current limited or otherwise controlled so thatundesired heating of the target tissue or surrounding (non-target)tissue does not occur. In a presently preferred embodiment of thepresent invention, current limiting inductors are placed in series witheach independent electrode terminal, where the inductance of theinductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously in U.S. Pat.No. 5,697,909, the complete disclosure of which is incorporated hereinby reference. Additionally, current limiting resistors may be selected.Preferably, these resistors will have a large positive temperaturecoefficient of resistance so that, as the current level begins to risefor any individual electrode terminal in contact with a low resistancemedium (e.g., saline irrigant or blood), the resistance of the currentlimiting resistor increases significantly, thereby minimizing the powerdelivery from said electrode terminal into the low resistance medium(e.g., saline irrigant or blood).

It should be clearly understood that the invention is not limited toelectrically isolated electrode terminals, or even to a plurality ofelectrode terminals. For example, the array of active electrodeterminals may be connected to a single lead that extends through thecatheter shaft to a power source of high frequency current.Alternatively, the instrument may incorporate a single electrode thatextends directly through the catheter shaft or is connected to a singlelead that extends to the power source. The active electrode(s) may haveball shapes (e.g., for tissue vaporization and desiccation), twizzleshapes (for vaporization and needle-like cutting), spring shapes (forrapid tissue debulking and desiccation), twisted metal shapes, annularor solid tube shapes or the like. Alternatively, the electrode(s) maycomprise a plurality of filaments, rigid or flexible brush electrode(s)(for debulking a tumor, such as a fibroid, bladder tumor or a prostateadenoma), side-effect brush electrode(s) on a lateral surface of theshaft, coiled electrode(s) or the like.

Referring to FIG. 1, an exemplary electrosurgical system 11 fortreatment of tissue in the spine will now be described in detail.Electrosurgical system 11 generally comprises an electrosurgicalhandpiece or probe 10 connected to a power supply 28 for providing highfrequency voltage to a target site and a fluid source 21 for supplyingelectrically conducting fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site. The endoscope maybe integral with probe 10, or it may be part of a separate instrument.The system 11 may also include a vacuum source (not shown) for couplingto a suction lumen or tube 205 (see FIG. 2) in the probe 10 foraspirating the target site.

As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of electrode terminals 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the electrode terminals 58 to power supply 28. The electrodeterminals 58 are electrically isolated from each other and each of theterminals 58 is connected to an active or passive control network withinpower supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conducting fluid 50 tothe target site. Fluid supply tube 15 may be connected to a suitablepump (not shown), if desired.

Power supply 28 has an operator controllable voltage level adjustment 30to change the applied voltage level, which is observable at a voltagelevel display 32. Power supply 28 also includes first, second and thirdfoot pedals 37, 38, 39 and a cable 36 which is removably coupled topower supply 28. The foot pedals 37, 38, 39 allow the surgeon toremotely adjust the energy level applied to electrode terminals 58. Inan exemplary embodiment, first foot pedal 37 is used to place the powersupply into the “ablation” mode and second foot pedal 38 places powersupply 28 into the “sub-ablation” mode (e.g., coagulation or contractionof tissue). The third foot pedal 39 allows the user to adjust thevoltage level within the “ablation” mode. In the ablation mode, asufficient voltage is applied to the electrode terminals to establishthe requisite conditions for molecular dissociation of the tissue (i.e.,vaporizing a portion of the electrically conductive fluid, ionizingcharged particles within the vapor layer and accelerating these chargedparticles against the tissue). As discussed above, the requisite voltagelevel for ablation will vary depending on the number, size, shape andspacing of the electrodes, the distance in which the electrodes extendfrom the support member, etc. Once the surgeon places the power supplyin the “ablation” mode, voltage level adjustment 30 or third foot pedal39 may be used to adjust the voltage level to adjust the degree oraggressiveness of the ablation.

Of course, it will be recognized that the voltage and modality of thepower supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

In the subablation mode, the power supply 28 applies a low enoughvoltage to the electrode terminals to avoid vaporization of theelectrically conductive fluid and subsequent molecular dissociation ofthe tissue. The surgeon may automatically toggle the power supplybetween the ablation and sub-ablation modes by alternatively stepping onfoot pedals 37, 38, respectively. In some embodiments, this allows thesurgeon to quickly move between coagulation/thermal heating and ablationin situ, without having to remove his/her concentration from thesurgical field or without having to request an assistant to switch thepower supply. By way of example, as the surgeon is sculpting soft tissuein the ablation mode, the probe typically will simultaneously sealand/or coagulation small severed vessels within the tissue. However,larger vessels, or vessels with high fluid pressures (e.g., arterialvessels) may not be sealed in the ablation mode. Accordingly, thesurgeon can simply step on foot pedal 38, automatically lowering thevoltage level below the threshold level for ablation, and applysufficient pressure onto the severed vessel for a sufficient period oftime to seal and/or coagulate the vessel. After this is completed, thesurgeon may quickly move back into the ablation mode by stepping on footpedal 37.

Referring now to FIGS. 2 and 3, a representative high frequency powersupply for use according to the principles of the present invention willnow be described. The high frequency power supply of the presentinvention is configured to apply a high frequency voltage of about 10 to500 volts RMS between one or more electrode terminals (and/orcoagulation electrode) and one or more return electrodes. In theexemplary embodiment, the power supply applies about 70-350 volts RMS inthe ablation mode and about 20 to 90 volts in a subablation mode,preferably 45 to 70 volts in the subablation mode (these values will, ofcourse, vary depending on the probe configuration attached to the powersupply and the desired mode of operation).

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the probe tip. The power source allows the userto select the voltage level according to the specific requirements of aparticular procedure, e.g., arthroscopic surgery, dermatologicalprocedure, ophthalmic procedures, open surgery or other endoscopicsurgery procedure.

As shown in FIG. 2, the power supply generally comprises a radiofrequency (RF) power oscillator 100 having output connections forcoupling via a power output signal 102 to the load impedance, which isrepresented by the electrode assembly when the electrosurgical probe isin use. In the representative embodiment, the RF oscillator operates atabout 100 kHz. The RF oscillator is not limited to this frequency andmay operate at frequencies of about 300 kHz to 600 kHz. In particular,for cardiac applications, the RF oscillator will preferably operate inthe range of about 400 kHz to about 600 kHz. The RF oscillator willgenerally supply a square wave signal with a crest factor of about 1 to2. Of course, this signal may be a sine wave signal or other suitablewave signal depending on the application and other factors, such as thevoltage applied, the number and geometry of the electrodes, etc. Thepower output signal 102 is designed to incur minimal voltage decrease(i.e., sag) under load. This improves the applied voltage to theelectrode terminals and the return electrode, which improves the rate ofvolumetric removal (ablation) of tissue.

Power is supplied to the oscillator 100 by a switching power supply 104coupled between the power line and the RF oscillator rather than aconventional transformer. The switching power supply 140 allows thegenerator to achieve high peak power output without the large size andweight of a bulky transformer. The architecture of the switching powersupply also has been designed to reduce electromagnetic noise such thatU.S. and foreign EMI requirements are met. This architecture comprises azero voltage switching or crossing, which causes the transistors to turnON and OFF when the voltage is zero. Therefore, the electromagneticnoise produced by the transistors switching is vastly reduced. In anexemplary embodiment, the switching power supply 104 operates at about100 kHz.

A controller 106 coupled to the operator controls 105 (i.e., foot pedalsand voltage selector) and display 116, is connected to a control inputof the switching power supply 104 for adjusting the generator outputpower by supply voltage variation. The controller 106 may be amicroprocessor or an integrated circuit. The power supply may alsoinclude one or more current sensors 112 for detecting the outputcurrent. The power supply is preferably housed within a metal casingwhich provides a durable enclosure for the electrical componentstherein. In addition, the metal casing reduces the electromagnetic noisegenerated within the power supply because the grounded metal casingfunctions as a “Faraday shield”, thereby shielding the environment frominternal sources of electromagnetic noise.

The power supply generally comprises a main or mother board containinggeneric electrical components required for many different surgicalprocedures (e.g., arthroscopy, urology, general surgery, dermatology,neurosurgery, etc.), and a daughter board containing applicationspecific current-limiting circuitry (e.g., inductors, resistors,capacitors and the like). The daughter board is coupled to the motherboard by a detachable multi-pin connector to allow convenient conversionof the power supply to, e.g., applications requiring a different currentlimiting circuit design. For arthroscopy, for example, the daughterboard preferably comprises a plurality of inductors of about 200 to 400microhenries, usually about 300 microhenries, for each of the channelssupplying current to the electrode terminals 02 (see FIG. 2).

Alternatively, in one embodiment, current limiting inductors are placedin series with each independent electrode terminal, where the inductanceof the inductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously inco-pending PCT application No. PCT/US94/05168, the complete disclosureof which is incorporated herein by reference. Additionally, currentlimiting resistors may be selected. Preferably, these resistors willhave a large positive temperature coefficient of resistance so that, asthe current level begins to rise for any individual electrode terminalin contact with a low resistance medium (e.g., saline irrigant orconductive gel), the resistance of the current limiting resistorincreases significantly, thereby minimizing the power delivery from saidelectrode terminal into the low resistance medium (e.g., saline irrigantor conductive gel). Power output signal may also be coupled to aplurality of current limiting elements 96, which are preferably locatedon the daughter board since the current limiting elements may varydepending on the application. A more complete description of arepresentative power supply can be found in commonly assigned U.S. Pat.application Ser. No. 09/058,571, previously incorporated herein byreference.

FIGS. 4-6 illustrate an exemplary electrosurgical probe 20 constructedaccording to the principles of the present invention. As shown in FIG.4, probe 90 generally includes an elongated shaft 100 which may beflexible or rigid, a handle 204 coupled to the proximal end of shaft 100and an electrode support member 102 coupled to the distal end of shaft100. Shaft 100 preferably comprises an electrically conducting material,usually metal, which is selected from the group comprising tungsten,stainless steel alloys, platinum or its alloys, titanium or its alloys,molybdenum or its alloys, and nickel or its alloys. In this embodiment,shaft 100 includes an electrically insulating jacket 108, which istypically formed as one or more electrically insulating sheaths orcoatings, such as polytetrafluoroethylene, polyimide, and the like. Theprovision of the electrically insulating jacket over the shaft preventsdirect electrical contact between these metal elements and any adjacentbody structure or the surgeon. Such direct electrical contact between abody structure (e.g., tendon) and an exposed electrode could result inunwanted heating and necrosis of the structure at the point of contactcausing necrosis. Alternatively, the return electrode may comprise anannular band coupled to an insulating shaft and having a connectorextending within the shaft to its proximal end.

Handle 204 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. Handle 204 defines aninner cavity (not shown) that houses the electrical connections 250(FIG. 6), and provides a suitable interface for connection to anelectrical connecting cable 22 (see FIG. 1). Electrode support member102 extends from the distal end of shaft 100 (usually about 1 to 20 mm),and provides support for a plurality of electrically isolated electrodeterminals 104 (see FIG. 5). As shown in FIG. 4, a fluid tube 233 extendsthrough an opening in handle 204, and includes a connector 235 forconnection to a fluid supply source, for supplying electricallyconductive fluid to the target site. Depending on the configuration ofthe distal surface of shaft 100, fluid tube 233 may extend through asingle lumen (not shown) in shaft 100, or it may be coupled to aplurality of lumens (also not shown) that extend through shaft 100 to aplurality of openings at its distal end. In the representativeembodiment, fluid tube 239 is a plastic tubing that extends along theexterior of shaft 100 to a point just distal of return electrode 112(see FIG. 5). In this embodiment, the fluid is directed through anopening 237 past return electrode 112 to the electrode terminals 104.Probe 20 may also include a valve 17 (FIG. 1) or equivalent structurefor controlling the flow rate of the electrically conducting fluid tothe target site.

As shown in FIG. 4, the distal portion of shaft 100 is preferably bentto improve access to the operative site of the tissue being treated.Electrode support member 102 has a substantially planar tissue treatmentsurface 212 (FIG. 5) that is usually at an angle of about 10 to 90degrees relative to the longitudinal axis of shaft 100, preferably about30 to 60 degrees and more preferably about 45 degrees. In alternativeembodiments, the distal portion of shaft 100 comprises a flexiblematerial which can be deflected relative to the longitudinal axis of theshaft. Such deflection may be selectively induced by mechanical tensionof a pull wire, for example, or by a shape memory wire that expands orcontracts by externally applied temperature changes. A more completedescription of this embodiment can be found in U.S. Pat. No. 5,697,909,the complete disclosure of which has previously been incorporated hereinby reference. Alternatively, the shaft 100 of the present invention maybe bent by the physician to the appropriate angle using a conventionalbending tool or the like.

In the embodiment shown in FIGS. 4-6, probe 20 includes a returnelectrode 112 for completing the current path between electrodeterminals 104 and a high frequency power supply 28 (see FIG. 1). Asshown, return electrode 112 preferably comprises an exposed portion ofshaft 100 shaped as an annular conductive band near the distal end ofshaft 100 slightly proximal to tissue treatment surface 212 of electrodesupport member 102, typically about 0.5 to 10 mm and more preferablyabout 1 to 10 mm. Return electrode 112 or shaft 100 is coupled to aconnector 258 that extends to the proximal end of probe 10, where it issuitably connected to power supply 10 (FIG. 1).

As shown in FIG. 4, return electrode 112 is not directly connected toelectrode terminals 104. To complete this current path so that electrodeterminals 104 are electrically connected to return electrode 112,electrically conducting fluid (e.g., isotonic saline) is caused to flowtherebetween. In the representative embodiment, the electricallyconducting fluid is delivered through fluid tube 233 to opening 237, asdescribed above. Alternatively, the fluid may be delivered by a fluiddelivery element (not shown) that is separate from probe 20. Inarthroscopic surgery, for example, the body cavity will be flooded withisotonic saline and the probe 90 will be introduced into this floodedcavity. Electrically conducting fluid will be continually resupplied tomaintain the conduction path between return electrode 112 and electrodeterminals 104. In other embodiments, the distal portion of probe 20 maybe dipped into a source of electrically conductive fluid, such as a gelor isotonic saline, prior to positioning at the target site. Applicanthas found that the surface tension of the fluid and/or the viscousnature of a gel allows the conductive fluid to remain around the activeand return electrodes for long enough to complete its function accordingto the present invention, as described below. Alternatively, theconductive fluid, such as a gel, may be applied directly to the targetsite.

In alternative embodiments, the fluid path may be formed in probe 90 by,for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (see FIGS. 8Aand 8B). This annular gap may be formed near the perimeter of the shaft100 such that the electrically conducting fluid tends to flow radiallyinward towards the target site, or it may be formed towards the centerof shaft 100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or having a pumping device), is coupled to probe 90 via afluid supply tube (not shown) that may or may not have a controllablevalve. A more complete description of an electrosurgical probeincorporating one or more fluid lumen(s) can be found in U.S. Pat. No.5,697,281, the complete disclosure of which has previously beenincorporated herein by reference.

Referring to FIG. 5, the electrically isolated electrode terminals 104are spaced apart over tissue treatment surface 212 of electrode supportmember 102. The tissue treatment surface and individual electrodeterminals 104 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface212 has a circular cross-sectional shape with a diameter in the range of1 mm to 20. The individual electrode terminals 104 preferably extendoutward from tissue treatment surface 212 by a distance of about 0.1 to4 mm, usually about 0.2 to 2 mm. Applicant has found that thisconfiguration increases the high electric field intensities andassociated current densities around electrode terminals 104 tofacilitate the ablation of tissue as described in detail above.

In the embodiment of FIGS. 4-6, the probe includes a single, largeropening 209 in the center of tissue treatment surface 212, and aplurality of electrode terminals (e.g., about 3-15) around the perimeterof surface 212 (see FIG. 5). Alternatively, the probe may include asingle, annular, or partially annular, electrode terminal at theperimeter of the tissue treatment surface. The central opening 209 iscoupled to a suction lumen (not shown) within shaft 100 and a suctiontube 211 (FIG. 4) for aspirating tissue, fluids and/or gases from thetarget site. In this embodiment, the electrically conductive fluidgenerally flows radially inward past electrode terminals 104 and thenback through the opening 209. Aspirating the electrically conductivefluid during surgery allows the surgeon to see the target site, and itprevents the fluid from flowing into the patient's body.

Of course, it will be recognized that the distal tip of probe may have avariety of different configurations. For example, the probe may includea plurality of openings 209 around the outer perimeter of tissuetreatment surface 212 (see FIG. 7B). In this embodiment, the electrodeterminals 104 extend distally from the center of tissue treatmentsurface 212 such that they are located radially inward from openings209. The openings are suitably coupled to fluid tube 233 for deliveringelectrically conductive fluid to the target site, and suction tube 211for aspirating the fluid after it has completed the conductive pathbetween the return electrode 112 and the electrode terminals 104.

FIG. 6 illustrates the electrical connections 250 within handle 204 forcoupling electrode terminals 104 and return electrode 112 to the powersupply 28. As shown, a plurality of wires 252 extend through shaft 100to couple terminals 104 to a plurality of pins 254, which are pluggedinto a connector block 256 for coupling to a connecting cable 22 (FIG.1). Similarly, return electrode 112 is coupled to connector block 256via a wire 258 and a plug 260.

According to the present invention, the probe 20 further includes anidentification element that is characteristic of the particularelectrode assembly so that the same power supply 28 can be used fordifferent electrosurgical operations. In one embodiment, for example,the probe 20 includes a voltage reduction element or a voltage reductioncircuit for reducing the voltage applied between the electrode terminals104 and the return electrode 112. The voltage reduction element servesto reduce the voltage applied by the power supply so that the voltagebetween the electrode terminals and the return electrode is low enoughto avoid excessive power dissipation into the electrically conductingmedium and/or ablation of the soft tissue at the target site. In someembodiments, the voltage reduction element allows the power supply 28 toapply two different voltages simultaneously to two different electrodes(see FIG. 15D). In other embodiments, the voltage reduction elementprimarily allows the electrosurgical probe 90 to be compatible withother ArthroCare generators that are adapted to apply higher voltagesfor ablation or vaporization of tissue. For thermal heating orcoagulation of tissue, for example, the voltage reduction element willserve to reduce a voltage of about 100 to 170 volts rms (which is asetting of 1 or 2 on the ArthroCare Model 970 and 980 (i.e., 2000)Generators) to about 45 to 60 volts rms, which is a suitable voltage forcoagulation of tissue without ablation (e.g., molecular dissociation) ofthe tissue.

Of course, for some procedures, the probe will typically not require avoltage reduction element. Alternatively, the probe may include avoltage increasing element or circuit, if desired. Alternatively oradditionally, the cable 22 that couples the power supply 10 to the probe90 may be used as a voltage reduction element. The cable has an inherentcapacitance that can be used to reduce the power supply voltage if thecable is placed into the electrical circuit between the power supply,the electrode terminals and the return electrode. In this embodiment,the cable 22 may be used alone, or in combination with one of thevoltage reduction elements discussed above, e.g., a capacitor. Further,it should be noted that the present invention can be used with a powersupply that is adapted to apply a voltage within the selected range fortreatment of tissue. In this embodiment, a voltage reduction element orcircuitry may not be desired.

FIGS. 8A-8C schematically illustrate the distal portion of threedifferent embodiments of probe 90 according to the present invention. Asshown in 8A, electrode terminals 104 are anchored in a support matrix102 of suitable insulating material (e.g., silicone or a ceramic orglass material, such as alumina, zirconia and the like) which could beformed at the time of manufacture in a flat, hemispherical or othershape according to the requirements of a particular procedure. Thepreferred support matrix material is alumina, available from KyoceraIndustrial Ceramics Corporation, Elkgrove, Ill., because of its highthermal conductivity, good electrically insulative properties, highflexural modulus, resistance to carbon tracking, biocompatibility, andhigh melting point. The support matrix 102 is adhesively joined to atubular support member 78 that extends most or all of the distancebetween matrix 102 and the proximal end of probe 90. Tubular member 78preferably comprises an electrically insulating material, such as anepoxy or silicone-based material.

In a preferred construction technique, electrode terminals 104 extendthrough pre-formed openings in the support matrix 102 so that theyprotrude above tissue treatment surface 212 by the desired distance. Theelectrodes are then bonded to the tissue treatment surface 212 ofsupport matrix 102, typically by an inorganic sealing material 80.Sealing material 80 is selected to provide effective electricalinsulation, and good adhesion to both the alumina matrix 102 and theplatinum or titanium electrode terminals. Sealing material 80additionally should have a compatible thermal expansion coefficient anda melting point well below that of platinum or titanium and alumina orzirconia, typically being a glass or glass ceramic.

In the embodiment shown in FIG. 8A, return electrode 112 comprises anannular member positioned around the exterior of shaft 100 of probe 90.Return electrode 90 may fully or partially circumscribe tubular supportmember 78 to form an annular gap 54 therebetween for flow ofelectrically conducting liquid 50 therethrough, as discussed below. Gap54 preferably has a width in the range of 0.25 mm to 4 mm.Alternatively, probe may include a plurality of longitudinal ribsbetween support member 78 and return electrode 112 to form a pluralityof fluid lumens extending along the perimeter of shaft 100. In thisembodiment, the plurality of lumens will extend to a plurality ofopenings.

Return electrode 112 is disposed within an electrically insulativejacket 18, which is typically formed as one or more electricallyinsulative sheaths or coatings, such as polytetrafluoroethylene,polyamide, and the like. The provision of the electrically insulativejacket 18 over return electrode 112 prevents direct electrical contactbetween return electrode 56 and any adjacent body structure. Such directelectrical contact between a body structure (e.g., tendon) and anexposed electrode member 112 could result in unwanted heating andnecrosis of the structure at the point of contact causing necrosis.

As shown in FIG. 8A, return electrode 112 is not directly connected toelectrode terminals 104. To complete this current path so that terminals104 are electrically connected to return electrode 112, electricallyconducting liquid 50 (e.g., isotonic saline) is caused to flow alongfluid path(s) 83. Fluid path 83 is formed by annular gap 54 betweenouter return electrode 112 and tubular support member. The electricallyconducting liquid 50 flowing through fluid path 83 provides a pathwayfor electrical current flow between electrode terminals 104 and returnelectrode 112, as illustrated by the current flux lines 60 in FIG. 8A.When a voltage difference is applied between electrode terminals 104 andreturn electrode 112, high electric field intensities will be generatedat the distal tips of terminals 104 with current flow from terminals 104through the target tissue to the return electrode, the high electricfield intensities causing ablation of tissue 52 in zone 88.

FIG. 8B illustrates another alternative embodiment of electrosurgicalprobe 90 which has a return electrode 112 positioned within tubularmember 78. Return electrode 112 is preferably a tubular member definingan inner lumen 57 for allowing electrically conducting liquid 50 (e.g.,isotonic saline) to flow therethrough in electrical contact with returnelectrode 112. In this embodiment, a voltage difference is appliedbetween electrode terminals 104 and return electrode 112 resulting inelectrical current flow through the electrically conducting liquid 50 asshown by current flux lines 60. As a result of the applied voltagedifference and concomitant high electric field intensities at the tipsof electrode terminals 104, tissue 52 becomes ablated or transected inzone 88.

FIG. 8C illustrates another embodiment of probe 90 that is a combinationof the embodiments in FIGS. 8A and 8B. As shown, this probe includesboth an inner lumen 57 and an outer gap or plurality of outer lumens 54for flow of electrically conductive fluid. In this embodiment, thereturn electrode 112 may be positioned within tubular member 78 as inFIG. 8B, outside of tubular member 78 as in FIG. 8A, or in bothlocations.

In some embodiments, the probe 20 will also include one or moreaspiration electrode(s) coupled to the aspiration lumen for inhibitingclogging during aspiration of tissue fragments from the surgical site.As shown in FIG. 9, one or more of the active electrode terminals 104may comprise loop electrodes 140 that extend across distal opening 209of the suction lumen within shaft 100. In the representative embodiment,two of the electrode terminals 104 comprise loop electrodes 140 thatcross over the distal opening 209. Of course, it will be recognized thata variety of different configurations are possible, such as a singleloop electrode, or multiple loop electrodes having differentconfigurations than shown. In addition, the electrodes may have shapesother than loops, such as the coiled configurations shown in FIGS. 10and 11. Alternatively, the electrodes may be formed within suction lumenproximal to the distal opening 209, as shown in FIG. 13. The mainfunction of loop electrodes 140 is to ablate portions of tissue that aredrawn into the suction lumen to prevent clogging of the lumen.

In some embodiments, loop electrodes 140 are electrically isolated fromthe other electrode terminals 104, which can be referred to hereinafteras the ablation electrodes 104. In other embodiments, the loopelectrodes 140 and electrode terminals 104 may be electrically connectedto each other such that both are activated together. Loop electrodes 140may or may not be electrically isolated from each other. Loop electrodes140 will usually extend only about 0.05 to 4 mm, preferably about 0.1 to1 mm from the tissue treatment surface of electrode support member 104.

Referring now to FIGS. 10 and 11, alternative embodiments for aspirationelectrodes will now be described. As shown in FIG. 10, the aspirationelectrodes may comprise a pair of coiled electrodes 150 that extendacross distal opening 209 of the suction lumen. The larger surface areaof the coiled electrodes 150 usually increases the effectiveness of theelectrodes 150 on tissue fragments passing through opening 209. In FIG.11, the aspiration electrode comprises a single coiled electrode 152passing across the distal opening 209 of suction lumen. This singleelectrode 152 may be sufficient to inhibit clogging of the suctionlumen. Alternatively, the aspiration electrodes may be positioned withinthe suction lumen proximal to the distal opening 209. Preferably, theseelectrodes are close to opening 209 so that tissue does not clog theopening 209 before it reaches electrodes 154. In this embodiment, aseparate return electrode 156 may be provided within the suction lumento confine the electric currents therein.

Referring to FIG. 13, another embodiment of the present inventionincorporates an aspiration electrode 160 within the aspiration lumen 162of the probe. As shown, the electrode 160 is positioned just proximal ofdistal opening 209 so that the tissue fragments are ablated as theyenter lumen 162. In the representation embodiment, the aspirationelectrode 160 comprises a loop electrode that stretches across theaspiration lumen 162. However, it will be recognized that many otherconfigurations are possible. In this embodiment, the return electrode164 is located outside of the probe as in the previously embodiments.Alternatively, the return electrode(s) may be located within theaspiration lumen 162 with the aspiration electrode 160. For example, theinner insulating coating 163 may be exposed at portions within the lumen162 to provide a conductive path between this exposed portion of returnelectrode 164 and the aspiration electrode 160. The latter embodimenthas the advantage of confining the electric currents to within theaspiration lumen. In addition, in dry fields in which the conductivefluid is delivered to the target site, it is usually easier to maintaina conductive fluid path between the active and return electrodes in thelatter embodiment because the conductive fluid is aspirated through theaspiration lumen 162 along with the tissue fragments.

Referring to FIG. 12, another embodiment of the present inventionincorporates a wire mesh electrode 600 extending across the distalportion of aspiration lumen 162. As shown, mesh electrode 600 includes aplurality of openings 602 to allow fluids and tissue fragments to flowthrough into aspiration lumen 162. The size of the openings 602 willvary depending on a variety of factors. The mesh electrode may becoupled to the distal or proximal surfaces of ceramic support member102. Wire mesh electrode 600 comprises a conductive material, such astitanium, tantalum, steel, stainless steel, tungsten, copper, gold orthe like. In the representative embodiment, wire mesh electrode 600comprises a different material having a different electric potentialthan the active electrode terminal(s) 104. Preferably, mesh electrode600 comprises steel and electrode terminal(s) comprises tungsten.Applicant has found that a slight variance in the electrochemicalpotential of mesh electrode 600 and electrode terminal(s) 104 improvesthe performance of the device. Of course, it will be recognized that themesh electrode may be electrically insulated from active electrodeterminal(s) as in previous embodiments.

Referring now to FIGS. 14A-14C, an alternative embodiment incorporatinga metal screen 610 is illustrated. As shown, metal screen 610 has aplurality of peripheral openings 612 for receiving electrode terminals104, and a plurality of inner openings 614 for allowing aspiration offluid and tissue through opening 609 of the aspiration lumen. As shown,screen 610 is press fitted over electrode terminals 104 and then adheredto shaft 100 of probe 20. Similar to the mesh electrode embodiment,metal screen 610 may comprise a variety of conductive metals, such astitanium, tantalum, steel, stainless steel, tungsten, copper, gold orthe like. In the representative embodiment, metal screen 610 is coupleddirectly to, or integral with, active electrode terminal(s) 104. In thisembodiment, the active electrode terminal(s) 104 and the metal screen610 are electrically coupled to each other.

FIGS. 15A-15D illustrate embodiments of an electrosurgical probe 350specifically designed for the treatment of herniated or diseased spinaldiscs. Referring to FIG. 15A, probe 350 comprises an electricallyconductive shaft 352, a handle 354 coupled to the proximal end of shaft352 and an electrically insulating support member 356 at the distal endof shaft 352. Probe 350 further includes a shrink wrapped insulatingsleeve 358 over shaft 352, and exposed portion of shaft 352 thatfunctions as the return electrode 360. In the representative embodiment,probe 350 comprises a plurality of active electrodes 362 extending fromthe distal end of support member 356. As shown, return electrode 360 isspaced a further distance from active electrodes 362 than in theembodiments described above. In this embodiment, the return electrode360 is spaced a distance of about 2.0 to 50 mm, preferably about 5 to 25mm. In addition, return electrode 360 has a larger exposed surface areathan in previous embodiments, having a length in the range of about 2.0to 40 mm, preferably about 5 to 20 mm. Accordingly, electric currentpassing from active electrodes 362 to return electrode 360 will follow acurrent flow path 370 that is further away from shaft 352 than in theprevious embodiments. In some applications, this current flow path 370results in a deeper current penetration into the surrounding tissue withthe same voltage level, and thus increased thermal heating of thetissue. As discussed above, this increased thermal heating may haveadvantages in some applications of treating disc abnormalities.Typically, it is desired to achieve a tissue temperature in the range ofabout 60° C. to 100° C. to a depth of about 0.2 to 5 mm, usually about 1to 2 mm. The voltage required for this thermal damage will partly dependon the electrode configurations, the conductivity of the tissue and thearea immediately surrounding the electrodes, the time period in whichthe voltage is applied and the depth of tissue damage desired. With theelectrode configurations described in FIGS. 15A-15D, the voltage levelfor thermal heating will usually be in the range of about 20 to 300volts rms, preferably about 60 to 200 volts rms. The peak-to-peakvoltages for thermal heating with a square wave form having a crestfactor of about 2 are typically in the range of about 40 to 600 voltspeak-to-peak, preferably about 120 to 400 volts peak-to-peak. The higherthe voltage is within this range, the less time required. If the voltageis too high, however, the surface tissue may be vaporized, debulked orablated, which is undesirable.

In alternative embodiments, the electrosurgical system used inconjunction with probe 350 may include a dispersive return electrode 450(see FIG. 16) for switching between bipolar and monopolar modes. In thisembodiment, the system will switch between an ablation mode, where thedispersive pad 450 is deactivated and voltage is applied between activeand return electrodes 362, 360, and a subablation or thermal heatingmode, where the active electrode(s) 362 and deactivated and voltage isapplied between the dispersive pad 450 and the return electrode 360. Inthe subablation mode, a lower voltage is typically applied and thereturn electrode 360 functions as the active electrode to providethermal heating and/or coagulation of tissue surrounding returnelectrode 360.

FIG. 15B illustrates yet another embodiment of the present invention. Asshown, electrosurgical probe 350 comprises an electrode assembly 372having one or more active electrode(s) 362 and a proximally spacedreturn electrode 360 as in previous embodiments. Return electrode 360 istypically spaced about 0.5 to 25 mm, preferably 1.0 to 5.0 mm from theactive electrode(s) 362, and has an exposed length of about 1 to 20 mm.In addition, electrode assembly 372 includes two additional electrodes374, 376 spaced axially on either side of return electrode 360.Electrodes 374, 376 are typically spaced about 0.5 to 25 mm, preferablyabout 1 to 5 mm from return electrode 360. In the representativeembodiment, the additional electrodes 374, 376 are exposed portions ofshaft 352, and the return electrode 360 is electrically insulated fromshaft 352 such that a voltage difference may be applied betweenelectrodes 374, 376 and electrode 360. In this embodiment, probe 350 maybe used in at least two different modes, an ablation mode and asubablation or thermal heating mode. In the ablation mode, voltage isapplied between active electrode(s) 362 and return electrode 360 in thepresence of electrically conductive fluid, as described above. In theablation mode, electrodes 374, 376 are deactivated. In the thermalheating or coagulation mode, active electrode(s) 362 are deactivated anda voltage difference is applied between electrodes 374, 376 andelectrode 360 such that a high frequency current 370 flows therebetween,as shown in FIG. 15B. In the thermal heating mode, a lower voltage istypically applied below the threshold for plasma formation and ablation,but sufficient to cause some thermal damage to the tissue immediatelysurrounding the electrodes without vaporizing or otherwise debulkingthis tissue so that the current 370 provides thermal heating and/orcoagulation of tissue surrounding electrodes 360, 372, 374.

FIG. 15C illustrates another embodiment of probe 350 incorporating anelectrode assembly 372 having one or more active electrode(s) 362 and aproximally spaced return electrode 360 as in previous embodiments.Return electrode 360 is typically spaced about 0.5 to 25 mm, preferably1.0 to 5.0 mm from the active electrode(s) 362, and has an exposedlength of about 1 to 20 mm. In addition, electrode assembly 372 includesa second active electrode 380 separated from return electrode 360 by anelectrically insulating spacer 382. In this embodiment, handle 354includes a switch 384 for toggling probe 350 between at least twodifferent modes, an ablation mode and a subablation or thermal heatingmode. In the ablation mode, voltage is applied between activeelectrode(s) 362 and return electrode 360 in the presence ofelectrically conductive fluid, as described above. In the ablation mode,electrode 380 deactivated. In the thermal heating or coagulation mode,active electrode(s) 362 may be deactivated and a voltage difference isapplied between electrode 380 and electrode 360 such that a highfrequency current 370 flows therebetween. Alternatively, activeelectrode(s) 362 may not be deactivated as the higher resistance of thesmaller electrodes may automatically send the electric current toelectrode 380 without having to physically decouple electrode(s) 362from the circuit. In the thermal heating mode, a lower voltage istypically applied below the threshold for plasma formation and ablation,but sufficient to cause some thermal damage to the tissue immediatelysurrounding the electrodes without vaporizing or otherwise debulkingthis tissue so that the current 370 provides thermal heating and/orcoagulation of tissue surrounding electrodes 360, 380.

Of course, it will be recognized that a variety of other embodiments maybe used to accomplish similar functions as the embodiments describedabove. For example, electrosurgical probe 350 may include a plurality ofhelical bands formed around shaft 352, with one or more of the helicalbands having an electrode coupled to the portion of the band such thatone or more electrodes are formed on shaft 352 spaced axially from eachother.

FIG. 15D illustrates another embodiment of the invention designed forchanneling through tissue and creating lesions therein to treat spinaldiscs and/or snoring and sleep apnea. As shown, probe 350 is similar tothe probe in FIG. 15C having a return electrode 360 and a third,coagulation electrode 380 spaced proximally from the return electrode360. In this embodiment, active electrode 362 comprises a singleelectrode wire extending distally from insulating support member 356. Ofcourse, the active electrode 362 may have a variety of configurations toincrease the current densities on its surfaces, e.g., a conical shapetapering to a distal point, a hollow cylinder, loop electrode and thelike. In the representative embodiment, support members 356 and 382 areconstructed of inorganic material, such as ceramic, glass, silicone andthe like. The proximal support member 382 may also comprise a moreconventional organic material as this support member 382 will generallynot be in the presence of a plasma that would otherwise etch or wearaway an organic material.

The probe 350 in FIG. 15D does not include a switching element. In thisembodiment, all three electrodes are activated when the power supply isactivated. The return electrode 360 has an opposite polarity from theactive and coagulation electrodes 362, 380 such that current 370 flowsfrom the latter electrodes to the return electrode 360 as shown. In thepreferred embodiment, the electrosurgical system includes a voltagereduction element or a voltage reduction circuit for reducing thevoltage applied between the coagulation electrode 380 and returnelectrode 360. The voltage reduction element allows the power supply 28to, in effect, apply two different voltages simultaneously to twodifferent electrodes. Thus, for channeling through tissue, the operatormay apply a voltage sufficient to provide ablation of the tissue at thetip of the probe (i.e., tissue adjacent to the active electrode 362). Atthe same time, the voltage applied to the coagulation electrode 380 willbe insufficient to ablate tissue. For thermal heating or coagulation oftissue, for example, the voltage reduction element will serve to reducea voltage of about 100 to 300 volts rms to about 45 to 90 volts rms,which is a suitable voltage for coagulation of tissue without ablation(e.g., molecular dissociation) of the tissue.

In the representative embodiment, the voltage reduction element is acapacitor (not shown) coupled to the power supply and coagulationelectrode 380. The capacitor usually has a capacitance of about 200 to500 pF (at 500 volts) and preferably about 300 to 350 pF (at 500 volts).Of course, the capacitor may be located in other places within thesystem, such as in, or distributed along the length of, the cable, thegenerator, the connector, etc. In addition, it will be recognized thatother voltage reduction elements, such as diodes, transistors,inductors, resistors, capacitors or combinations thereof, may be used inconjunction with the present invention. For example, the probe 350 mayinclude a coded resistor (not shown) that is constructed to lower thevoltage applied between the return and coagulation electrodes 360, 380.In addition, electrical circuits may be employed for this purpose.

Of course, for some procedures, the probe will typically not require avoltage reduction element. Alternatively, the probe may include avoltage increasing element or circuit, if desired. Alternatively oradditionally, the cable 22 that couples the power supply 10 to the probe90 may be used as a voltage reduction element. The cable has an inherentcapacitance that can be used to reduce the power supply voltage if thecable is placed into the electrical circuit between the power supply,the electrode terminals and the return electrode. In this embodiment,the cable 22 may be used alone, or in combination with one of thevoltage reduction elements discussed above, e.g., a capacitor. Further,it should be noted that the present invention can be used with a powersupply that is adapted to apply two different voltages within theselected range for treatment of tissue. In this embodiment, a voltagereduction element or circuitry may not be desired.

In one specific embodiment, the probe 350 is manufactured by firstinserting an electrode wire (active electrode 362) through a ceramictube (insulating member 360) such that a distal portion of the wireextends through the distal portion of the tube, and bonding the wire tothe tube, typically with an appropriate epoxy. A stainless steel tube(return electrode 356) is then placed over the proximal portion of theceramic tube, and a wire (e.g., nickel wire) is bonded, typically byspot welding, to the inside surface of the stainless steel tube. Thestainless steel tube is coupled to the ceramic tube by epoxy, and thedevice is cured in an oven or other suitable heat source. A secondceramic tube (insulating member 382) is then placed inside of theproximal portion of the stainless steel tube, and bonded in a similarmanner. The shaft 358 is then bonded to the proximal portion of thesecond ceramic tube, and an insulating sleeve (e.g. polyimide) iswrapped around shaft 358 such that only a distal portion of the shaft isexposed (i.e., coagulation electrode 380). The nickel wire connectionwill extend through the center of shaft 358 to connect return electrode356 to the power supply. The active electrode 362 may form a distalportion of shaft 358, or it may also have a connector extending throughshaft 358 to the power supply.

In use, the physician positions active electrode 362 adjacent to thetissue surface to be treated (i.e., a spinal disc). The power supply isactivated to provide an ablation voltage between active and returnelectrodes 362, 360 and a coagulation or thermal heating voltage betweencoagulation and return electrodes 360, 380. An electrically conductivefluid is then provided around active electrode 362, and in the junctionbetween the active and return electrodes 360, 362 to provide a currentflow path therebetween. This may be accomplished in a variety ofmanners, as discussed above. The active electrode 362 is then advancedthrough the space left by the ablated tissue to form a channel in thedisc. During ablation, the electric current between the coagulation andreturn electrode is typically insufficient to cause any damage to thesurface of the tissue as these electrodes pass through the tissuesurface into the channel created by active electrode 362. Once thephysician has formed the channel to the appropriate depth, he or shewill cease advancement of the active electrode, and will either hold theinstrument in place for 5 to 30 seconds, or will immediately remove thedistal tip of the instrument from the channel (see detailed discussionof this below). In either event, when the active electrode is no longeradvancing, it will eventually stop ablating tissue.

Prior to entering the channel formed by the active electrode 362, anopen circuit exists between return and coagulation electrodes 360, 380.Once coagulation electrode 380 enters this channel, electric currentwill flow from coagulation electrode 380, through the tissue surroundingthe channel, to return electrode 360. This electric current will heatthe tissue immediately surrounding the channel to coagulate any severedvessels at the surface of the channel. If the physician desires, theinstrument may be held within the channel for a period of time to createa lesion around the channel, as discussed in more detail below.

FIG. 16 illustrates yet another embodiment of an electrosurgical system440 incorporating a dispersive return pad 450 attached to theelectrosurgical probe 400. In this embodiment, the invention functionsin the bipolar mode as described above. In addition, the system 440 mayfunction in a monopolar mode in which a high frequency voltagedifference is applied between the active electrode(s) 410, and thedispersive return pad 450. In the exemplary embodiment, the pad 450 andthe probe 400 are coupled together, and are both disposable, single-useitems. The pad 450 includes an electrical connector 452 that extendsinto handle 404 of probe 400 for direct connection to the power supply.Of course, the invention would also be operable with a standard returnpad that connects directly to the power supply. In this embodiment, thepower supply 460 will include a switch, e.g., a foot pedal 462, forswitching between the monopolar and bipolar modes. In the bipolar mode,the return path on the power supply is coupled to return electrode 408on probe 400, as described above. In the monopolar mode, the return pathon the power supply is coupled to connector 452 of pad 450, activeelectrode(s) 410 are decoupled from the electrical circuit, and returnelectrode 408 functions as the active electrode This allows the surgeonto switch between bipolar and monopolar modes during, or prior to, thesurgical. In some cases, it may be desirable to operate in the monopolarmode to provide deeper current penetration and, thus, a greater thermalheating of the tissue surrounding the return electrodes. In other cases,such as ablation of tissue, the bipolar modality may be preferable tolimit the current penetration to the tissue.

In one configuration, the dispersive return pad 450 is adapted forcoupling to an external surface of the patient in a region substantiallyclose to the target region. For example, during the treatment of tissuein the head and neck, the dispersive return pad is designed andconstructed for placement in or around the patient's shoulder, upperback or upper chest region. This design limits the current path throughthe patient's body to the head and neck area, which minimizes the damagethat may be generated by unwanted current paths in the patient's body,particularly by limiting current flow through the patient's heart. Thereturn pad is also designed to minimize the current densities at thepad, to thereby minimize patient skin burns in the region where the padis attached.

Referring to FIG. 17, the electrosurgical device according to thepresent invention may also be configured as a catheter system 400. Asshown in FIG. 17, a catheter system 400 generally comprises anelectrosurgical catheter 460 connected to a power supply 28 by aninterconnecting cable 486 for providing high frequency voltage to atarget tissue and an irrigant reservoir or source 600 for providingelectrically conducting fluid to the target site. Catheter 460 generallycomprises an elongate, flexible shaft body 462 including a tissueremoving or ablating region 464 at the distal end of body 462. Theproximal portion of catheter 460 includes a multi-lumen fitment 614which provides for interconnections between lumens and electrical leadswithin catheter 460 and conduits and cables proximal to fitment 614. Byway of example, a catheter electrical connector 496 is removablyconnected to a distal cable connector 494 which, in turn, is removablyconnectable to generator 28 through connector 492. One or moreelectrically conducting lead wires (not shown) within catheter 460extend between one or more active electrodes 463 and a coagulationelectrode 467 at tissue ablating region 464 and one or morecorresponding electrical terminals (also not shown) in catheterconnector 496 via active electrode cable branch 487. Similarly, a returnelectrode 466 at tissue ablating region 464 are coupled to a returnelectrode cable branch 489 of catheter connector 496 by lead wires (notshown). Of course, a single cable branch (not shown) may be used forboth active and return electrodes.

Catheter body 462 may include reinforcing fibers or braids (not shown)in the walls of at least the distal ablation region 464 of body 462 toprovide responsive torque control for rotation of electrode terminalsduring tissue engagement. This rigid portion of the catheter body 462preferably extends only about 7 to 10 mm while the remainder of thecatheter body 462 is flexible to provide good trackability duringadvancement and positioning of the electrodes adjacent target tissue.

Conductive fluid 30 is provided to tissue ablation region 464 ofcatheter 460 via a lumen (not shown in FIG. 17) within catheter 460.Fluid is supplied to lumen from the source along a conductive fluidsupply line 602 and a conduit 603, which is coupled to the innercatheter lumen at multi-lumen fitment 114. The source of conductivefluid (e.g., isotonic saline) may be an irrigant pump system (not shown)or a gravity-driven supply, such as an irrigant reservoir 600 positionedseveral feet above the level of the patient and tissue ablating region8. A control valve 604 may be positioned at the interface of fluidsupply line 602 and conduit 603 to allow manual control of the flow rateof electrically conductive fluid 30. Alternatively, a metering pump orflow regulator may be used to precisely control the flow rate of theconductive fluid.

System 400 further includes an aspiration or vacuum system (not shown)to aspirate liquids and gases from the target site. The aspirationsystem will usually comprise a source of vacuum coupled to fitment 614by a aspiration connector 605.

The present invention is particularly useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. As shown in FIGS. 18-23, a percutaneous penetration270 is made in the patients' back 272 so that the superior lamina 274can be accessed. Typically, a small needle (not shown) is used initiallyto localize the disc space level, and a guidewire (not shown) isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina 274. Sequential cannulated dilators 276 are inserted over theguide wire and each other to provide a hole from the incision 220 to thelamina 274. The first dilator may be used to “palpate” the lamina 274,assuring proper location of its tip between the spinous process andfacet complex just above the inferior edge of the lamina 274. As shownin FIG. 21, a tubular retractor 278 is then passed over the largestdilator down to the lamina 274. The dilators 276 are removed,establishing an operating corridor within the tubular retractor 278.

As shown in FIG. 19, an endoscope 280 is then inserted into the tubularretractor 278 and a ring clamp 282 is used to secure the endoscope 280.Typically, the formation of the operating corridor within retractor 278requires the removal of soft tissue, muscle or other types of tissuethat were forced into this corridor as the dilators 276 and retractor278 were advanced down to the lamina 274. This tissue is usually removedwith mechanical instruments, such as pituitary rongeurs, curettes,graspers, cutters, drills, microdebriders and the like. Unfortunately,these mechanical instruments greatly lengthen and increase thecomplexity of the procedure. In addition, these instruments sever bloodvessels within this tissue, usually causing profuse bleeding thatobstructs the surgeon's view of the target site.

According to one aspect of the present invention, an electrosurgicalprobe or catheter 284 as described above is introduced into theoperating corridor within the retractor 278 to remove the soft tissue,muscle and other obstructions from this corridor so that the surgeon caneasily access and visualization the lamina 274. Once the surgeon hasreached has introduced the probe 284, electrically conductive fluid 285is delivered through tube 233 and opening 237 to the tissue (see FIG.2). The fluid flows past the return electrode 112 to the electrodeterminals 104 at the distal end of the shaft. The rate of fluid flow iscontrolled with valve 17 (FIG. 1) such that the zone between the tissueand electrode support 102 is constantly immersed in the fluid. The powersupply 28 is then turned on and adjusted such that a high frequencyvoltage difference is applied between electrode terminals 104 and returnelectrode 112. The electrically conductive fluid provides the conductionpath (see current flux lines) between electrode terminals 104 and thereturn electrode 112.

The high frequency voltage is sufficient to convert the electricallyconductive fluid (not shown) between the target tissue and electrodeterminal(s) 104 into an ionized vapor layer or plasma (not shown). As aresult of the applied voltage difference between electrode terminal(s)104 and the target tissue (i.e., the voltage gradient across the plasmalayer), charged particles in the plasma (viz., electrons) areaccelerated towards the tissue. At sufficiently high voltagedifferences, these charged particles gain sufficient energy to causedissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases, such as oxygen, nitrogen, carbon dioxide, hydrogen andmethane. The short range of the accelerated charged particles within thetissue confines the molecular dissociation process to the surface layerto minimize damage and necrosis to the underlying tissue.

During the process, the gases will be aspirated through opening 209 andsuction tube 211 to a vacuum source. In addition, excess electricallyconductive fluid, and other fluids (e.g., blood) will be aspirated fromthe operating corridor to facilitate the surgeon's view. During ablationof the tissue, the residual heat generated by the current flux lines(typically less than 150° C.), will usually be sufficient to coagulateany severed blood vessels at the site. If not, the surgeon may switchthe power supply 28 into the coagulation mode by lowering the voltage toa level below the threshold for fluid vaporization, as discussed above.This simultaneous hemostasis results in less bleeding and facilitatesthe surgeon's ability to perform the procedure.

Another advantage of the present invention is the ability to preciselyablate soft tissue without causing necrosis or thermal damage to theunderlying and surrounding tissues, nerves or bone. In addition, thevoltage can be controlled so that the energy directed to the target siteis insufficient to ablate the lamina 274 so that the surgeon canliterally clean the tissue off the lamina 274, without ablating orotherwise effecting significant damage to the lamina.

Referring now to FIGS. 20 and 21, once the operating corridor issufficiently cleared, a laminotomy and medial facetectomy isaccomplished either with conventional techniques (e.g., Kerrison punchor a high speed drill) or with the electrosurgical probe 284 asdiscussed above. After the nerve root is identified, medical retractioncan be achieved with a retractor 288, or the present invention can beused to precisely ablate the disc. If necessary, epidural veins arecauterized either automatically or with the coagulation mode of thepresent invention. If an annulotomy is necessary, it can be accomplishedwith a microknife or the ablation mechanism of the present inventionwhile protecting the nerve root with the retractor 288. The herniateddisc 290 is then removed with a pituitary rongeur in a standard fashion,or once again through ablation as described above.

In another embodiment, the present invention involves a channelingtechnique in which small holes or channels are formed within the disc290, and thermal energy is applied to the tissue surface immediatelysurrounding these holes or channels to cause thermal damage to thetissue surface, thereby stiffening and debulking the surrounding tissuestructure of the disc. Applicant has discovered that such stiffening ofthe tissue structure in the disc helps to reduce the pressure appliedagainst the spinal nerves by the disc, thereby relieving back and neckpain.

As shown in FIG. 21, the electrosurgical instrument 350 is introduced tothe target site at the disc 290 as described above, or in anotherpercutaneous manner (see FIGS. 23-25 below). The electrode assembly 351is positioned adjacent to or against the disc surface, and electricallyconductive fluid is delivered to the target site, as described above.Alternatively, the conductive fluid is applied to the target site, orthe distal end of probe 350 is dipped into conductive fluid or gel priorto introducing the probe 350 into the patient. The power supply 28 isthen activated and adjusted such that a high frequency voltagedifference is applied to the electrode assembly as described above.

Depending on the procedure, the surgeon may translate the electrodesrelative to the target disc tissue to form holes, channels, stripes,divots, craters or the like within the disc. In addition, the surgeonmay purposely create some thermal damage within these holes, or channelsto form scar tissue that will stiffen and debulk the disc. In oneembodiment, the physician axially translates the electrode assembly 351into the disc tissue as the tissue is volumetrically removed to form oneor more holes 702 therein (see also FIG. 22). The holes 702 willtypically have a diameter of less than 2 mm, preferably less than 1 mm.In another embodiment (not shown), the physician translates the activeelectrode across the outer surface of the disc to form one or morechannels or troughs. Applicant has found that the present invention canquickly and cleanly create such holes, divots or channels in tissue withthe cold ablation technology described herein. A more completedescription of methods for forming holes or channels in tissue can befound in U.S. Pat. No. 5,683,366, the complete disclosure of which isincorporated herein by reference for all purposes.

FIG. 22 is a more detailed viewed of the probe 350 of FIG. 15D forming ahole 702 in a disc 290. Hole 702 is preferably formed with the methodsdescribed in detail above. Namely, a high frequency voltage differenceis applied between active and return electrodes 362, 360, respectively,in the presence of an electrically conductive fluid such that anelectric current 361 passes from the active electrode 362, through theconductive fluid, to the return electrode 360. As shown in FIG. 22, thiswill result in shallow or no current penetration into the disc tissue704. The fluid may be delivered to the target site, applied directly tothe target site, or the distal end of the probe may be dipped into thefluid prior to the procedure. The voltage is sufficient to vaporize thefluid around active electrode 362 to form a plasma with sufficientenergy to effect molecular dissociation of the tissue. The distal end ofthe probe 350 is then axially advanced through the tissue as the tissueis removed by the plasma in front of the probe 350. The holes 702 willtypically have a depth D in the range of about 0.5 to 2.5 cm, preferablyabout 1.2 to 1.8 cm, and a diameter d of about 0.5 to 5 mm, preferablyabout 1.0 to 3.0 mm. The exact diameter will, of course, depend on thediameter of the electrosurgical probe used for the procedure.

During the formation of each hole 702, the conductive fluid betweenactive and return electrodes 362, 360 will generally minimize currentflow into the surrounding tissue, thereby minimizing thermal damage tothe tissue. Therefore, severed blood vessels on the surface 705 of thehole 702 may not be coagulated as the electrodes 362 advance through thetissue. In addition, in some procedures, it may be desired to thermallydamage the surface 705 of the hole 702 to stiffen the tissue. For thesereasons, it may be desired in some procedures to increase the thermaldamage caused to the tissue surrounding hole 702. In the embodimentshown in FIG. 15D, it may be necessary to either: (1) withdraw the probe350 slowly from hole 702 after coagulation electrode 380 has at leastpartially advanced past the outer surface of the disc tissue 704 intothe hole 702 (as shown in FIG. 22); or (2) hold the probe 350 within thehole 702 for a period of time, e.g., on the order of 1 to 30 seconds.Once the coagulation electrode is in contact with, or adjacent to,tissue, electric current 755 flows through the tissue surrounding hole702 and creates thermal damage therein. The coagulation and returnelectrodes 380, 360 both have relatively large, smooth exposed surfacesto minimize high current densities at their surfaces, which minimizesdamage to the surface 705 of hole. Meanwhile, the size and spacing ofthese electrodes 360, 380 allows for relatively deep current penetrationinto the tissue 704. In the representative embodiment, the thermalnecrosis 706 will extend about 1.0 to 5.0 mm from surface 705 of hole702. In this embodiment, the probe may include one or more temperaturesensors (not shown) on probe coupled to one or more temperature displayson the power supply 28 such that the physician is aware of thetemperature within the hole 702 during the procedure.

In other embodiments, the physician switches the electrosurgical systemfrom the ablation mode to the subablation or thermal heating mode afterthe hole 702 has been formed. This is typically accomplished by pressinga switch or foot pedal to reduce the voltage applied to a level belowthe threshold required for ablation for the particular electrodeconfiguration and the conductive fluid being used in the procedure (asdescribed above). In the subablation mode, the physician will thenremove the distal end of the probe 350 from the hole 702. As the probeis withdrawn, high frequency current flows from the active electrodes362 through the surrounding tissue to the return electrode 360. Thiscurrent flow heats the tissue and coagulates severed blood vessels atsurface 704.

In another embodiment, the electrosurgical probe of the presentinvention can be used to ablate and/or contract soft tissue within thedisc 290 to allow the annulus 292 to repair itself to preventreoccurrence of this procedure. For tissue contraction, a sufficientvoltage difference is applied between the electrode terminals 104 andthe return electrode 112 to elevate the tissue temperature from normalbody temperatures (e.g., 37° C.) to temperatures in the range of 45° C.to 90° C., preferably in the range from 60° C. to 70° C. Thistemperature elevation causes contraction of the collagen connectivefibers within the disc tissue so that the disc 290 withdraws into theannulus 292.

In one method of tissue contraction according to the present invention,an electrically conductive fluid is delivered to the target site asdescribed above, and heated to a sufficient temperature to inducecontraction or shrinkage of the collagen fibers in the target tissue.The electrically conducting fluid is heated to a temperature sufficientto substantially irreversibly contract the collagen fibers, whichgenerally requires a tissue temperature in the range of about 45° C. to90° C., usually about 60° C. to 70° C. The fluid is heated by applyinghigh frequency electrical energy to the electrode terminal(s) in contactwith the electrically conducting fluid. The current emanating from theelectrode terminal(s) 104 heats the fluid and generates a jet or plumeof heated fluid, which is directed towards the target tissue. The heatedfluid elevates the temperature of the collagen sufficiently to causehydrothermal shrinkage of the collagen fibers. The return electrode 112draws the electric current away from the tissue site to limit the depthof penetration of the current into the tissue, thereby inhibitingmolecular dissociation and breakdown of the collagen tissue andminimizing or completely avoiding damage to surrounding and underlyingtissue structures beyond the target tissue site. In an exemplaryembodiment, the electrode terminal(s) 104 are held away from the tissuea sufficient distance such that the RF current does not pass into thetissue at all, but rather passes through the electrically conductingfluid back to the return electrode. In this embodiment, the primarymechanism for imparting energy to the tissue is the heated fluid, ratherthan the electric current.

In an alternative embodiment, the electrode terminal(s) 104 are broughtinto contact with, or close proximity to, the target tissue so that theelectric current passes directly into the tissue to a selected depth. Inthis embodiment, the return electrode draws the electric current awayfrom the tissue site to limit its depth of penetration into the tissue.Applicant has discovered that the depth of current penetration also canbe varied with the electrosurgical system of the present invention bychanging the frequency of the voltage applied to the electrode terminaland the return electrode. This is because the electrical impedance oftissue is known to decrease with increasing frequency due to theelectrical properties of cell membranes which surround electricallyconductive cellular fluid. At lower frequencies (e.g., less than 350kHz), the higher tissue impedance, the presence of the return electrodeand the electrode terminal configuration of the present invention(discussed in detail below) cause the current flux lines to penetrateless deeply resulting in a smaller depth of tissue heating. In anexemplary embodiment, an operating frequency of about 100 to 200 kHz isapplied to the electrode terminal(s) to obtain shallow depths ofcollagen shrinkage (e.g., usually less than 1.5 mm and preferably lessthan 0.5 mm).

In another aspect of the invention, the size (e.g., diameter orprincipal dimension) of the electrode terminals employed for treatingthe tissue are selected according to the intended depth of tissuetreatment. As described previously in copending patent application PCTInternational Application, U.S. National Phase Ser. No. PCT/US94/05168,the depth of current penetration into tissue increases with increasingdimensions of an individual active electrode (assuming other factorsremain constant, such as the frequency of the electric current, thereturn electrode configuration, etc.). The depth of current penetration(which refers to the depth at which the current density is sufficient toeffect a change in the tissue, such as collagen shrinkage, irreversiblenecrosis, etc.) is on the order of the active electrode diameter for thebipolar configuration of the present invention and operating at afrequency of about 100 kHz to about 200 kHz. Accordingly, forapplications requiring a smaller depth of current penetration, one ormore electrode terminals of smaller dimensions would be selected.Conversely, for applications requiring a greater depth of currentpenetration, one or more electrode terminals of larger dimensions wouldbe selected.

FIGS. 23-25 illustrate another system and method for treating swollen orherniated spinal discs according to the present invention. In thisprocedure, an electrosurgical probe 700 comprises a long, thinneedle-like shaft 702 (e.g., on the order of about 1 mm in diameter orless) that can be percutaneously introduced anteriorly through theabdomen or thorax, or through the patient's back directly into thespine. The shaft 702 may or may not be flexible, depending on the methodof access chosen by the physician. The probe shaft 702 will include oneor more active electrode(s) 704 for applying electrical energy totissues within the spine. The probe 700 may include one or more returnelectrode(s) 706, or the return electrode may be positioned on thepatient's back, as a dispersive pad (not shown). As discussed below,however, a bipolar design is preferable.

As shown in FIG. 23, the distal portion of shaft 702 is introducedanteriorly through a small percutaneous penetration into the annulus 710of the target spinal disc. To facilitate this process, the distal end ofshaft 702 may taper down to a sharper point (e.g., a needle), which canthen be retracted to expose active electrode(s) 704. Alternatively, theelectrodes may be formed around the surface of the tapered distalportion of shaft (not shown). In either embodiment, the distal end ofshaft is delivered through the annulus 710 to the target nucleuspulposis 290, which may be herniated, extruded, non-extruded, or simplyswollen. As shown in FIG. 24, high frequency voltage is applied betweenactive electrode(s) 704 and return electrode(s) 710 to heat thesurrounding collagen to suitable temperatures for contraction (i.e.,typically about 55° C. to about 70° C.). As discussed above, thisprocedure may be accomplished with a monopolar configuration, as well.However, applicant has found that the bipolar configuration shown inFIGS. 23-25 provides enhanced control of the high frequency current,which reduces the risk of spinal nerve damage.

As shown in FIGS. 24 and 25, once the pulposis 290 has been sufficientcontracted to retract from impingement on the nerve 720, the probe 700is removed from the target site. In the representative embodiment, thehigh frequency voltage is applied between active and return electrode(s)704 706 as the probe is withdrawn through the annulus 710. This voltageis sufficient to cause contraction of the collagen fibers within theannulus 710, which allows the annulus 710 to contract around the holeformed by probe 700, thereby improving the healing of this hole. Thus,the probe 700 seals its own passage as it is withdrawn from the disc.

What is claimed is:
 1. A method for treating intervertebral discs:positioning an active electrode adjacent to, or within, a disc; applyinghigh frequency voltage between the active electrode and a returnelectrode, the high frequency voltage being sufficient to ablate thedisc tissue; during the applying step, advancing the active electrodeinto the disc tissue to generate a space within the disc tissue; andremoving the active electrode from the space within the disc tissue. 2.The method of claim 1 further comprising, during the removing step,applying high frequency voltage between the active and returnelectrodes, the high frequency voltage being sufficient to coagulateblood at the tissue surface surrounding the space.
 3. The method ofclaim 2 wherein the high frequency voltage during the applying step issufficient to thermally damage the surface of the disc tissuesurrounding the space.
 4. The method of claim 1 further comprisingproviding an electrically conductive fluid around the active electrodeand between the active and return electrodes prior to the applying step.5. The method of claim 4 wherein the providing step comprisespositioning the active and return electrodes within a supply ofelectrically conductive fluid and then positioning the active and returnelectrodes adjacent to the disc.
 6. The method of claim 4 wherein theproviding step comprises delivering the electrically conductive fluid tothe active and return electrodes.
 7. The method of claim 4 wherein theelectrically conductive fluid is a liquid.
 8. The method of claim 4further comprising generating a current flow path between the active andreturn electrodes with the electrically conductive fluid.
 9. The methodof claim 4 further comprising aspirating fluid from a region around theactive electrode.
 10. The method of claim 1 further comprising applyinga sufficient high frequency voltage difference between the active andreturn electrodes to effect molecular dissociation of at least a portionof the disc tissue during the advancing step.
 11. The method of claim 1wherein the applying step includes generating a voltage gradient betweenthe active and return electrodes, the voltage gradient being sufficientto create an electric field that breaks down the tissue throughmolecular dissociation.
 12. The method of claim 1 further comprisingapplying sufficient voltage to the active electrode in the presence ofan electrically conductive fluid to vaporize at least a portion of thefluid between the active electrode and the disc tissue.
 13. The methodof claim 12 further comprising accelerating charged particles from thevaporized fluid to the disc tissue to cause dissociation of themolecular bonds within the disc tissue.
 14. The method of claim 1further comprising axially translating the active electrode to form ahole through at least a portion of the disc tissue.
 15. The method ofclaim 1 further comprising transversely translating the active electroderelative to the disc tissue to form a channel along a surface of thedisc.
 16. The method of claim 1 wherein the space has a maximum lateraldimension less than about 2 mm.
 17. The method of claim 1 wherein thespace has a maximum lateral dimension less than about 1 mm.
 18. Themethod of claim 1 wherein the positioning step comprises positioning adistal portion of a shaft of an electrosurgical instrument within thedisc, wherein the active and return electrodes are both located on thedistal portion of the shaft.
 19. The method of claim 18 furthercomprising introducing at least the distal end portion of the shaftthrough a percutaneous penetration in the patient to the disc.
 20. Themethod of claim 18 wherein the active electrode is positioned adjacent atarget portion of the disc, the method further comprising locating thereturn electrode on the shaft such that, during the applying step,electric current flows from the active electrode away from the targetportion of the disc to the return electrode, wherein the returnelectrode is axially spaced at least about 1.0 mm from the activeelectrode.
 21. The method of claim 18 further comprising, after theapplying step, deactivating the active electrode and applying a highfrequency voltage difference between a second active electrode and oneor more return electrodes on the instrument shaft.
 22. The method ofclaim 21 wherein the instrument shaft comprises a second returnelectrode spaced proximally from the second active electrode, the methodcomprising, after the applying step, applying a high frequency voltagedifference between the second active electrode and the first and secondreturn electrodes.
 23. The method of claim 18 further comprising, afterthe applying step, deactivating the active electrode and applying a highfrequency voltage difference between the return electrode on theinstrument shaft and a dispersive return electrode coupled to anexternal surface of the patient.
 24. The method of claim 1 furthercomprising positioning the active and return electrodes within a nucleusof the disc and during the applying step, passing electric currentbetween the active and return electrodes through naturally occuringconductive fluid within the nucleus.